UNIVERSITY  OF  CALIFORNIA 

AT    LOS  ANGELES 


SOILS 


6515      1  3 


SOILS 


THEIR 


FORMATION,    PROPERTIES,    COMPOSITION,  AND 
RELATIONS  TO  CLIMATE  AND  PLANT  GROWTH 


IN  THE 


HUMID   AND  ARID  REGIONS 


BY 

E.  W.  HILGARD,  PH.D.,  LL.D., 

PROFESSOR  OF  AGRICULTURE   IN  THE  UNIVERSITY  OF  CALIFORNIA,  AND  DIRECTOR 
OF  THE  CALIFORNIA  AGRICULTURAL   EXPERIMENT   STATION 


THE  MACMILLAN  COMPANY 

LONDON:  MACMILLAN  &  CO.,  LTD. 


COPYRIGHT,  1906, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.  Published  July,  1906.  Reprinted 
August,  1907  ;  January,  1910;  April,  1911;  September,  1912; 
September,  1914;  January,  1918. 


Notfoooto 
Berwick  &  Smith  Co.,  Norwood,  Mass.,  U.S.A. 


SUMMARY  OF  CHAPTERS. 


ORIGIN  AND  FORMATION  OF  SOILS. 
Introduction. 
Chapter 


I.     Physical  Processes  of  Soil  Formation. 
II.     Chemical  Processes  of  Soil  Formation. 

III.  Chief  Soil-forming  Minerals. 

IV.  The  Various  Rocks  as  Soil-Formers. 

V.     Minor  Mineral  Ingredients  of  Soils.  Mineral  Fertilizers. 
Minerals  Injurious  to  Agriculture. 


2.  PHYSICS  OF  SOILS. 

Chapter          VI.     Physical  Composition  of  Soils. 

"  VII.     Density,  Pore  Space,  and  Volume-Weight  of  Soils. 

"  VIII.  Soil  and  Subsoil  ;  Causes  and  Processes  of  Differen- 

tiation ;  Humus. 

"  IX.  Soil  and  Subsoil  ;  Organisms  Influencing  Soil-Con- 

ditions. Bacteria. 

"  X.     Soil  and  Subsoil  in  their  Relations  to  Vegetation. 

"  XI.  Water  of  Soils  ;  Hygroscopic  and  Capillary  Moisture. 

XII.  Water  of  Soils  ;  Surface,  Hydrostatic,  and  Ground- 
water  ;  Percolation. 

XIII.  Water  of  Soils  ;  Conservation  and  Regulation  of  Soil 

Moisture.     Irrigation. 

XIV.  Absorption  by  Soils  of  Solids  from  Solutions.  Absorp- 

tion of  Gases.     The  Air  of  Soils. 
"  XV.     Colors  of  Soils. 

"  XVI.     Climate. 

"          XVII.     Relations  of  Soils  and  Plant-Growth  to  Heat. 

3.  CHEMISTRY  OF  SOILS. 

Chapter  XVIII.     Physico-Chemical  Investigation  of  Soils  in   Relation 

to  Crop  Production. 
XIX.     Analysis  of    Virgin  Soils  by   Kxtraction  with  Strong 

Acids,  and  its  Interpretation. 
XX.     Soils  of  Arid  and  Humid  Regions. 
XXI.     Soils  of  Arid  and  Humid  Regions  continued. 
XXII.     Alkali  Soils,  their  Nature  and  Composition. 
"        XXIII.     Utilization  and  Reclamation  of  Alkali  Lands. 

iii 


iv  SUMMARY  OF  CHAPTERS. 

4.  Soiw  AND  NATIVE  VEGETATION. 

Chapter  XXIV.     Recognition  of    the  Character  of    Soils  from    their 

Native  Vegetation.     Mississippi. 

"          XXV.     Recognition  of  the   Character    of    Soils    from   their 
Native  Vegetation.  United  States  at  large,  Europe. 
"        XXVI.     Vegetation  of  Saline  and  Alkali  Lands. 


TABLE  OF  CONTENTS. 


PREFACE xxiii 

INTRODUCTION,  xxix. — Definition  of  Soils,  xxix.  — Elements  Constituting  the 
Earth's  Crust,  xxix.— Average  Quantitative  Composition  of  the  Earth's 
Crust,  xxix. — Clarke's  Table,  xxx. — Oxids  Constitute  Earth's  Crust,  xxx. 
— Elements  Important  to  Agriculture  ;  Table,  xxxi. — The  Volatile  Part 
of  Plants,  xxxii. 

CHAPTER  I. 

AGENCIES  OF  Son,  FORMATION,  i. — i.  Physical  Agencies,  i. — Effects  of 
Heat  and  Cold  on  Rocks,  i. — Unequal  Expansion  of  Crystals,  2. — Cleav- 
age of  Rocks,  3. — Effects  of  Freezing  Water,  3. — Glaciers  ;  Figure,  3. — 
Glacier  Flour  and  Mud,  4. — "  Green"  and  "White"  Rivers,  4. — 
Moraines,  5. — Action  of  Flowing  Water,  5. — Enormous  Result  of  Cor- 
rasion  and  Denudation,  6. — Effects  of  Winds,  8. — Dunes,  8. — Sand  and 
Dust  Storms  in  Deserts,  Continental  Plateaus  and  Plains,  8. — Loess  of 
China,  9. — Migration  of  Gobi  Lakes,  9. — Classification  of  Soils,  10. — 
Their  Physical  Constituents,  10. — Sedentary  or  Residual  Soils,  n.— 
Colluvial  Soils,  12. — Alluvial  Soils.  Diagram,  12. — Character  of  these 
Soil  Classes,  13. — Richness  of  Flood-plain  and  Delta  Lands,  14. — Low- 
ering of  the  Land  Surface  by  Soil  Formation,  15. 

CHAPTER  II. 

CHEMICAL  PROCESSES  OF  SOIL  FORMATION,  16. — 2.  Chemical  Disintegra- 
tions or  Decomposition,  16. — Ingredients  of  the  Atmosphere,  16. — Effects 
of  Water  ;  of  Carbonic  Acid,  17. — Carbonated  water  a  universal  solvent, 
17. — Ammonic  carbonate,  effect  on  silicates,  18. — Action  of  oxygen  ;  on 
ferrous  compounds,  18. — Action  of  Plants  and  their  Remnants,  19. — A. 
Mechanical  ;  Force  of  Root  Penetration,  19. — B.  Chemical  ;  Action  of 
Root  Secretions,  19. — Bacterial  Action,  20. — Humification,  20. — Causes 
Influencing  Chemical  Action  and  Decomposition,  21. — Heat  and  Mois- 
ture, 21. — Influence  of  Rainfall  on  Soil-Formation,  22.  — Leaching  of  the 
Land,  22. — Residual  Soils,  22. — Drain  Waters  ;  River  Waters.  Tables 
of  Solid  Contents,  22.— Amount  of  Dissolved  Matters  Carried  into  the 
Sea  ;  Amount  of  Sediment,  24. — Sea  Water,  Composition  of  ;  Waters  of 
Land-locked  Lakes,  25. — Results  of  Insufficient  Rainfall  ;  Alkali 
Lands,  28. 

v 


vi  CONTENTS. 

CHAPTER  III. 

ROCK- AND  SOIL-FORMING  MINERALS,  29. — Quartz,  quartzite,  jasper,  horn- 
stone,  flint,  29. — Solubility  of  silica  in  water  ;  absorption  by  plants,  30. 
— Silicate  Minerals,  31. — Feldspars,  their  Kaolinization,  31. — Formation 
of  Clays,  33. — Hornblende  or  Amphibole,  Pyroxene  or  Augite,  33. — 
Their  Weathering  and  its  Products,  33. — Mica,  Muscovite  and  Biotite, 
35. — Hydromica,  Chlorite,  35. — Talc  and  Serpentine  ;  "  Soapstone  ",  36. 
The  Zeolites  ;  Exchange  of  Bases  in  Solutions,  36. — Importance  in 
Soils,  in  Rocks,  38. — Calcite,  Marble,  Limestones  ;  their  Origin,  39. — 
Impure  Limestones  as  Soil-Formers,  40. — Caves,  Sinkholes,  Stalactites, 
Tufa,  41. — Dolomite  ;  Magnesian  Limestones  as  Soil-Formers,  42. — 
Selenite,  Gypsum,  Land  Plaster ;  Agricultural  Uses,  42. — Iron  Spar, 
Limonite,  Hematite,  Magnetite,  44. — Reduction  of  Ferric  Hydrate  in 
Ill-drained  Soils,  45. 

CHAPTER  IV. 

THE  VARIOUS  ROCKS  AS  SOIL- FORMERS,  47.— General  Classification,  47. — 
Sedimentary,  Metamorphic,  Eruptive,  47. — Sedimentary  Rocks  ;  Lime- 
stones, Sandstones,  Clays,  Claystones,  Shales,  47. — Metamorphic  Rocks  : 
Formed  from  Sedimentary,  48. — Igneous  or  Eruptive  Rocks,  Basic  and 
Acidic,  49. — Generalities  Regarding  Soils  Derived  from  Various  Rocks, 
49. — Variations  in  Rocks  themselves.  Accessory  Minerals,  50. — 
Granites  ;  not  always  True  to  Name  ;  Sierra  Granites,  51. — Gneiss.  Mica- 
schist,  51. — Diorites,  51. — Diabases,  51. — Eruptive  Rocks  ;  Glassy  ones 
Weather  Slowly  ;  Basaltic  Oxidize  Rapidly,  52. — Red  Soils  of  Hawaii, 
Pacific  Northwest,  52. — Trachyte  Soils  ;  Light-colored,  rich  in  Potash. 
Rhyolites  generally  make  Poor  Soils,  53. — Sedimentary  Rocks,  53. — 
Limestones,  53. — "  A  Limestone  Country  is  a  Rich  Country,"  53. — 
Residual  Limestone  Soils;  from  "Rotten  Limestone"  of  Mississippi; 
Table,  54. — Shrinkage  of  Surface,  55. — Sandstone  Soils,  55. — Vary 
According  to  Cement,  and  Nature  of  Sand,  55. — Calcareous,  Dolomitic, 
Ferruginous,  Zeolitic,  56 — Clay-sandstones,  Claystones,  57. — Natural 
Clays,  57. — Great  Variety,  Enumeration  and  Definition,  58. — Colors  of 
Clays,  58, — Colloidal  Clay,  Nature  and  Properties,  59. — Plasticity  ; 
Kaolinite  Non-plastic,  59. — Causes  of  Plasticity,  60. — Separation  of 
Colloidal  Clay,  its  Properties,  61. — Effects  of  Alkali  Carbonates  on 
Clay,  62. 

CHAPTER   V. 

THE  MINOR  MINERAL  INGREDIENTS  OF  SOILS  ;  MINERAL  FERTILIZERS,  63. 
— Minerals  Injurious  to  Agriculture,  63. — Minerals  used  as  Fertilizers, 
63. — Apatite;  Phosphorites  of  the  U.  S.,  Antilles,  Africa,  Europe,  63. — 
Phosphatic  Iron  Ores,  "  Thomas  Slag,"  64. — Animal  Bones  ;  Composi- 
tion and  'Agricultural  Use,  64 — Vivianite,  Dufrenite,  65. — Chile  Salt- 
peter, 66.  Occurrence  in  Nevada,  California,  66. — Origin  of  Nitrate 
Deposits,  67. — Intensity  of  Nitrification  in  Arid  Climates,  68. — Potash 
Minerals,  68. — Feldspars  not  Available,  68. — Depletion  of  Lands  by 
Manufacture  of  Potashes,  69. — Discovery  of  Stassfurt  Salts,  69. — Origin 


CONTENTS.  vii 

of  these  Deposits,  70. — Nature  of  the  Salts,  71. — Kainit,  71. — Potash 
Salts  in  Alkali  Soils,  72. — Farmyard  or  Stable  Manure  ;  Chemical 
Composition,  Table,  72. — Efficacy  largely  due  to  Physical  Effects  in 
Soils,  73. — Green-manuring  a  Substitute  for  Stable  Manure,  74. — Ap- 
plication of  Stable  Manure  in  Humid  and  Arid  Climates,  74. — Mine- 
rals Unessential  or  Injurious  to  Soils,  75. — Iron  Pyrites,  Sulphur  Balls, 
75.  Occurrence  and  Recognition.  Remedies  75. — Halite  or  Common 
Salt,  76. — Recognition  of  Common  Salt,  76. — Mirabilite  or  Glauber's 
Salt  ;  in  Alkali  Lands  ;  not  very  Injurious,  77  — Trona  or  Urao  ;  Car- 
bonate of  Soda,  "Black  Alkali,"  77.  Injury  Caused  in  Soils,  78. — 
Epsomite  or  Epsom  Salt,  78. — Borax,  79. — Soluble  Salts  in  Irrigation 
Waters,  79. 

CHAPTER   VI. 

PHYSICAL  COMPOSITION  OF  SOILS,  83. — Clay  as  a  Soil  Ingredient,  83. — 
Amounts  of  Colloidal  Clay  in  Soils,  84. — Influence  of  Fine  Powders  on 
Plasticity,  85.— Rock  Powder  ;  Sand,  Silt  and  Dust,  ^.—  Weathering 
in  Humid  and  Arid  Regions,  86. — Sands  of  the  Humid  Regions,  86. — 
Sands  of  Arid  Regions  not  Sterile,  86. — Physical  Analysis  of  Soils,  88. 
— Use  of  Sieves.  Limits,  88. — Use  of  Water  for  Separating  Finest  Grain- 
Sizes,  89. — Elimination  of  Clay  by  Subsidence  and  Centrifugal  Method, 
Hydraulic  Elutriation,  90. — Schone's  Instrument,  90. — Churn  Elutriator 
with  Cylindrical  Tube,  91. — Figures  of  Same,  91. — Voder's  Centrifugal 
Elutriator,  92. — Number  of  Grain-sizes  Desirable,  93, — Results  of  such 
Analyses,  93. — Physical  Composition  Corresponding  to  Popular  Desig- 
nations of  Soil-Quality.  Table,  96. — Number  of  soil-grains  per  Gram, 
99. — Surface  Offered  by  various  Grain-sizes  ,99. — Influence  of  the  several 
Grain-si/.es  on  Soil  Texture,  100. — Ferric  Hydrate,  its  Effects  on  Clay, 
loo. — Other  Substances,  ioi. — Aluminic  Hydrate,  101. — Influence  of 
Granular  Sediments  upon  the  Tilling  Qualities  of  Soils,  102.  — "  Phy- 
sical "  Hard  pan,  103. — Putty  Soils,  103. — Dust  Soils  of  Washington  ; 
Table,  Physical  Analyses  of  Fine  Earth,  104. — Slow  Penetration  of 
Water,  105. — Effects  of  Coarse  Sand,  105. 

CHAPTER  VII. 

DENSITY,  PORE-SPACK  AND  VOLUME-WEIGHT  OF  SOILS,  107. — Density  of 
Soil  Minerals,  107. — No  Great  Variation,  107. — Volume-weight  most  Im- 
portant, 107. — Weight  per  Acre-foot,  107. — Air-space  in  Dry  Natural 
Soils.  Figure,  108. — May  be  Filled  with  Water,  108. — Effects  of  Tillage. 
Figures,  109. — Crumb  or  Flocculated  Structure  ;  Cements,  109.  —  How 
Nature  Tills,  ill. — Soils  of  the  Arid  Regions;  do  not  Crust,  112. — 
Changes  of  Soil-Volume  in  Wetting  and  Drying,  112.  —  Extent  of 
Shrinkage,  113. — Expansion  and  Contraction  of  Heavy  Clav  Soils. 
Figure,  113. — Contraction  of  Alkali  Soils  on  Wetting,  114.  — "Hog 
Wallows,"  114.  —  Physical  Analyses  of  such  Soils.  Table,  115.  —  Crumb- 
ling of  Calcareous  Clay  Soils  on  Drying,  116. — Yazoo  Bottom,  Port 
Hudson  Bluff,  116. — Loamy  and  Sandy  Soils,  117.  —  Formation  of  Sur- 
face Crusts,  Physical  Analyses,  117. — Effects  of  Frost  on  the  Soil; 
Heaving;  Ice-flowers,  118. 


viii  CONTENTS. 

CHAPTER  VIII. 

SOIL  AND  SUBSOIL;  CAUSES  AND  PROCESSES  OF  DIFFERENTATIATION 
HUMUS,  120.— Soil  and  Subsoil  ill-defined,  120. — The  Organic  and  Or- 
ganized Constituents  of  Soils,  120. — Humus  in  the  Surface  Soil,  120. — 
Soil  and  Subsoil  ;  Causes  of  their  Differentiation,  121. — Ulmin  Sub- 
stances or  Sour  Humus,  122. — Sour  Soils,  122. — Cultivation  Induces 
Acidity,  123. — Humin  Substances,  123. — Porosity  of  Humus,  124. — 
Physical  and  Chemical  Nature  of  the  Humus  Substances.  Table,  124. 
— Chemical  Nature,  125. — Progressive  Changes  and  Effect  on  Soils,  126. 
— The  Phases  of  Humification,  Wood  to  Anthracite;  Table,  127. — 
Amounts  of  Humus  and  Coal  formed  from  Vegetable  Matter,  128. — 
Figure,  From  Port  Hudson  Bluff,  128. — Conditions  of  Normal  Humifi- 
cation, 129. — Eremacausis  in  the  Arid  Regions,  129. — Black  Earth  of 
Russia  ;  Kosticheff's  Table,  130. — Losses  of  Humus  from  Cultivation 
and  Fallowing,  131. — Estimation  of  Humus  in  Soils;  Unreliability  of 
Combustion  Methods,  132. — Grandeau  Method,  "  Matiere  Noire,"  132. — 
Amounts  of  Humus  in  Soils,  133. — Humates  and  Ulmates,  134. — Mineral 
Ingredients  in  the  Humus,  134. — Functions  of  the  Unhumified  Organic 
Matter,  135. — The  Nitrogen  Content  of  Humus,  135. — Table  for  Arid 
and  Humid  Soils,  136. — Decrease  of  Nitrogen  Content  in  Humus  with 
Depth,  138. — Table,  Russian  River  Soils,  139. — Influence  of  the  Original 
Material  upon  the  Composition  of  Humus,  139. — Table  of  Snyder,  139. — 
Effect  of  Humus  in  rendering  Mineral  Plant  Food  Available,  140. 

CHAPTER  IX. 

SOIL  AND  SUBSOIL  (continued) ,  142. — ORGANISMS  INFLUENCING  SOIL-CONDI- 
TIONS. BACTERIA,  142. — Micro-organisms  of  the  Soil.  Bacteria,  Moulds, 
Ferments,  142. — Numbers  at  Various  Depths,  given  by  Early  Observers, 
142. — Investigations  of  Hohl ;  Mayo  and  Kinsley.  Tables,  143. — Multi- 
plication of  the  Bacteria,  144. — Aerobic  and  Anaerobic  Bacteria,  144. — 
Food  Materials  required,  145. — Functions  of  the  Bacteria,  145. — Nitrify- 
ing Bacteria.  Figures,  146. — Conditions  of  their  Activity.  Table,  146. 
— Effects  of  Aeration  and  Reduction,  147. — Unhumified  Organic  Matter 
does  not  Nitrify,  148 — Unhumified  Vegetable  Matter,  Functions  in  Soils, 
148. — Denitrifying  Bacteria.  Figures,  148. — Ammonia-forming  Bacte- 
ria. Figures,  149. — Alinit,  149. — Effects  of  Bacterial  Life  on  Physical 
Soil  Conditions,  149. — Root-bacteria,  or  Rhizobia  of  Legumes,  150. — 
Figures  of  Root  Excrescences  and  Corresponding  Bacteroids,  152. — 
Varieties  of  Forms,  154. — Mode  of  Infection,  154. — Cultural  Results, 
155. — Table  Showing  Increased  Production  by  Soil  Inoculation,  155. — 
Other  Nitrogen-absorbing  Bacteria,  156. — Distribution  of  Humus  in  the 
Surface  Soil,  157. — Fungi,  Moulds  and  Algae,  157. — Animal  Agencies — 
Earthworms,  Insects,  Burrowing  Quadrupeds,  158. 

CHAPTER  X. 

SOIL  AND  SUBSOIL  IN  THEIR  RELATIONS  TO  VEGETATION,  161. — Physical 
Effects  of  the  Percolation  of  Surface  Waters,  161. — Chemical  Effects  ; 
Calcareous  Subsoils  and  Hardpans,  161. — "  Rawness  "  of  Subsoils  in 


CONTENTS.  ix 

Humid  Climates,  162. — Subsoils  in  the  Arid  Region,  163. — Deep  Plow- 
ing and  Subsoiling  in  the  Arid  Region  ;  examples  of  Plant  growth 
on  Subsoils,  164. — Resistance  to  Drought,  167. — Root  System  in  the 
Humid  Region,  168.  Figures  of  the  Root  System  of  an  Eastern  (Wis- 
consin) Fruit  Tree,  168. — Comparison  of  Root  Development  in  the 
Arid  and  Humid  Regions,  169. — Prune  on  Peach  Root,  169. — Adapta- 
tion of  Humid  Species  to  Arid  Conditions,  169. — Grapes,  170. — Ken- 
tucky and  California  Maize,  175,  176.— Hops,  172. — Deep  Rooting  in  the 
Arid  Region,  174. — Goose  Foot  and  Figwort,  174. — Importance  of 
Proper  Substrata  in  the  Arid  Region,  175. — Injury  from  Impervious 
Substrata.  Figure,  177. — Faulty  I,ands  of  California.  Figure,  178. — 
Shattering  of  Dense  Substrata  by  Dynamite,  181. — Leachy  Substrata, 
182. — "Going-back"  of  Orchards,  182. — Hardpan,  Formation  and 
Varieties,  183. — Nature  of  the  Hardpan  Cements,  184. — Bog  Ore,  Moor- 
bedpan  and  Ortstein  ;  Calcareous  and  Alkali  Hardpan,  184. — The  Causes 
of  Hardpan,  185. — "  Plowsole,"  186. — Marly  Substrata,  186. 

CHAPTER  XI. 

THE  WATER  OF  SOILS.  HYGROSCOPIC  AND  CAPILLARY  MOISTURE,  188. — 
General  Properties,  188. — Physical  Factors  of  Water  compared  with 
other  Substances.  Table,  188. — Capillarity  or  Surface  Tension,  189.— 
Heat  Relations,  190. — Density,  190. —Specific  Heat  and  its  Effects,  190. 
Ice,  191. — Vaporization,  191. — Solvent  Power,  191. — Water-requirements 
of  Growing  Plants,  192.  — Evaporation  from  Plants  in  Different  Climates, 
192. — Relations  between  Evaporation  and  Plant  Growth.  Table,  193.— 
Fortier's  Experiments.  Figure,  194. — Different  Conditions  of  Soil 
Water,  196. — Hygroscopic  U'atcr  in  Soils  ;  Table,  196. — Influence  of 
Temperature  and  Air-Saturation,  197.- — Utility  of  Hygroscopic  Water 
to  Plant  Growth,  199. — Mayer's  Experiments,  200. — Summary,  200.— 
Capillary  Water,  201. — Ascent  of  Water  in  Soil-Columns.  Table,  202. 
— Ascent  in  Uniform  Sediments.  Figure,  204.  — Maximum  and  Minimum 
Water-holding  Power,  207. — Capillary  Water  held  at  different  Heights 
in  a  Soil  Column.  Table,  208. — Capillary  Action  in  Moist  Soils,  210. — 
Proportion  of  Soil  Moisture  Available  to  Plants,  21 1. — Moisture  Require- 
ments of  Crops  in  the  Arid  Region,  211. — Tables  of  Observations  in 
California,  214. 

CHAPTER    XII. 

SURFACE,  HYDROSTATIC  AND  GROUND  WATER.  PERCOLATION,  215. — 
Amount  of  Rainfall,  215. — Natural  Disposition  of  Rain  Water,  216.— 
The  Surface  Runoff,  216. — Washing-away  and  Gullying  in  tin-  Cotton 
States,  217. — Injury  in  the  Arid  Regions,  219. — Deforestation,  219. — 
Prevention  of  Injury  to  Cultivated  Lands  from  Excessive  Runoff,  220. 
Absorption  and  IHovcmcnts  of  U'atcr  in  Soils,  221. — Determination  of 
Rate  of  Percolation.  Diagram,  221. — Summary,  224. — Influence  of  Var- 
iety of  Grain-sizes,  224. — Table  of  King's  Experiments,  224. — Percola- 
tion in  Natural  Soils.  Figure,  225. — Ground  or  Bottom  Water,  227. — 
Lysimeters,  Surface  of  Ground  Water ;  Variations,  227. — Depth  of 


x  CONTENTS. 

Ground  Water  most  Favorable  to  Crops,  228. — Moisture  Supplied  by  Tap 
Roots,  229. — Reserve  of  Capillary  Water,  229. — Injurious  Rise  of  Bottom 
Water  from  Irrigation,  230. — Consequences  of  the  Swamping  of  Irrigated 
Lands  ;  Prevention,  231. — Permanent  Injury  to  certain  Lands,  231. — 
Reduction  of  Sulfates,  232. — Ferruginous  or  Red  Lands,  233. 

CHAPTER   XIII. 

WATER  OF  SOILS  ;  THE  REGULATION  AND  CONSERVATION  OF  SOIL  MOIST- 
URE ;  IRRIGATION,  234. — Loosening  of  the  Surface,  234. — Effects  of 
Underdrains  ;  Rain  on  Clay  Soils,  235. — Winter  Irrigation,  236. — 
Methods  of  Irrigation,  236. — Surface  Sprinkling,  237. — Flooding,  237. 
— Check  Flooding.  Furrow  Irrigation,  237,  238. — Figure  Showing  Pen- 
etration, 239. — Figure  Showing  Faulty  Irrigation  in  Sandy  Lands,  239. 
— Distance  between  Furrows  and  Ditches,  241. — Irrigation  by  Lateral 
Seepage,  242. — Basin  Irrigation  of  Trees  and  Vines  ;  Advantages  and 
Objections,  243. — Irrigation  from  Underground  Pipes,  245. — Quality  of 
Irrigation  Waters,  246. — Saline  Waters;  Figures  of  Effects  on  Orange 
Trees,  246. — Limits  of  Salinity,  246. — Mode  of  Using  Saline  Irrigation 
Waters  ;  Apparent  Paradox,  249. — Use  of  Drainage  Waters  for  Irrig- 
ation, 250. — "  Black  Alkali  "  Waters,  250. — Variations  in  the  Salinity 
of  Deep  and  Shallow  Wells,  250. — Muddy  Waters,  251. —  The  Duty  of 
Irrigation  Waters,  251. — Causes  of  Losses,  252. — Loss  by  Percolation. 
Figure,  252. — Evaporation,  253. — Tables  Showing  same  at  California 
Stations,  255. — Evaporation  in  Different  Climates  ;  Table,  255. — Evapo- 
ration from  Reservoirs  and  Ditches,  257. — Prevention  of  Evaporation  ; 
Protective  Surface  Layer,  257. — Illustrations  of  Effects  of  Tillage  ; 
Table,  258. — Evaporation  through  Roots  and  Leaves,  262. — Weeds 
waste  Moisture,  264. — Distribution  of  Moisture  in  Soils  as  Affected  by 
Vegetation,  264. — Forests  and  Steppes,  265. — Eucalyptus  for  Drying 
Wet  Lands,  265. — Mulching;  Effects  on  Temperature  and  Moisture;  266. 

CHAPTER    XIV. 

ABSORPTION  BY  SOILS  OF  SOLIDS  FROM  SOLUTIONS.  ABSORPTION  OF  GASES, 
AIR  OF  SOILS,  267. — Absorption  of  Solids,  267. — Desalation,  267. — Deco- 
lorization,  267. — Complexity  of  Soil-Action,  Physical  and  Chemical, 
268. — "  Purifying"  Action  of  Soils  on  Gases  and  Liquids,  269. — Waste 
of  Fertilizers,  269. — Variation  of  Absorptive  Power,  270. — Generalities 
Regarding  Chemical  Action  and  Exchange,  270. — Drain  Waters,  271. — 
Distinctions  not  Absolute,  272. — Absorption  or  Condensation  of  Gases 
by  the  Soil,  272. — Proof  of  Presence  of  Carbonic  and  Ammonia  Gases  in 
Soils,  273. — Absorption  of  Gases  by  Dry  Soils.  Figure,  274. — Composi- 
tion of  Gases  Absorbed  by  Various  Bodies  from  the  Air.  Table,  275. 
— Discussion  of  Table,  277. —  The  Air  of  Soils,  279. — Empty  Space  in 
Dry  Soils,  279. — Functions  of  Air  in  Soils,  279. — Insufficient  and  Ex- 
cessive Aeration,  280. — Composition  of  the  Free  Air  of  Soils,  280. — Car- 
bonic Dioxid  vs.  Oxygen,  281.  — Relation  to  Bacterial  and  Fungous 
Activity,  281. — Putrefactive  Processes,  282. 


CONTENTS.  xi 

CHAPTER  XV. 

COLORS  OF  SOILS,  283.— Black  Soils,  283. — "  Red  "  Soils,  284.— Origin  of 
Red  Tints,  285. — White  Soils,  285. — Differences  in  Arid  and  Humid 
Regions,  286.— White  Alkali  Spots,  286. 

CHAPTER  XVI. 

CUMATE,  287.— Heat  and  Moisture  Control  Climates,  287.— Climatic  Con- 
ditions, 287. — Ascertainment  and  Presentation  of  Temperature  Condi- 
tions, 288.— Annual  Mean  not  a  Good  Criterion,  289.— Extremes  of 
Temperature  are  most  Important,  289.— Seasonal  and  Monthly  Means, 
289. — Daily  Variations,  290. —  The  Rainfall,  290. — Annual  Rainfall  not 
a  Good  Criterion,  290.  Distribution  most  Important,  290. —  Winds,  291. 
— Heat  the  Cause  of  Winds,  291. — Trade  Winds,  291. — Cyclones,  292. 
Influence  of  the  Topography  on  Winds ;  Rains  to  Windward  of 
Mountains,  Arid  Climates  to  Leeward,  293.— General  Distribution  of 
Rainfall  on  the  Globe.  Figure,  294. — Ocean  Currents,  295. — The  Gulf 
Stream,  295. — The  Japan  Stream,  296. — Contrast  of  Climates  of  N.  W. 
America,  297. — Continental,  Coast  and  Insular  Climates,  297. — Subtropic. 
Arid  Belts,  298. — Utilization  of  the  Arid  Belts,  299. 

CHAPTER  XVII. 

RELATIONS  OF  SOILS  AND  PLANT  GROWTH  To  HEAT,  301. — Temperature  of 
Soils,  301. — Water  Exerts  Controlling  Influence,  301. — Cold  and  Warm 
Rains,  302. — Solar  Radiation,  302. — Penetration  of  the  Sun's  Heat  into 
the  Soil,  302. — Change  of  Temperature  with  Depth,  303. — Surface  Con- 
ditions that  Influence  Soil  Temperature,  303. — Heat  of  High  and  Low 
Intensity,  304. — Reflection  vs.  Dispersion  of  Heat,  304. — Influence  of 
Vegetation,  and  of  Mulches,  305.— Influence  of  the  Nature  of  the  Soil- 
Material,  306.  —  Influence  of  Evaporation,  307. — Formation  of  Dew,  307. 
— Dew  rarely  adds  Moisture,  308.  —  Dew  within  the  Soil,  308. — Plant 
Development  under  Different  Temperature-Conditions,  309. — Germin- 
ation of  Seeds  ;  Optimum  Temperature  for  each  Kind,  309. — Artificial 
Heating  of  Soils  ;  by  Steam  Pipes  or  Water,  310. 

CHAPTER  XVIII. 

PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS  IN  RELATION  TO  CROP 
PRODUCTION,  313. — Historical  Review  of  Soil  Investigation,  313. — 
Popular  Forecasts  of  Soil  Values,  313.  —  Cogency  of  Conclusions  Rased 
upon  Native  Growth,  314.  —  Ecological  Studies,  315.  —  Early  Soil  Surveys 
of  Kentucky,  Arkansas  and  Mississippi,  316.  —  Investigation  of  Cultivated 
Soils,  316. — Change  of  Views,  317. — Advantages  for  Soil  Study  offered 
by  Virgin  Lands,  318. — Practical  Utility  of  Soil  Analysis  ;  Permanent 
Value  vs.  Immediate  Productiveness,  319.  —  Phvsiral  and  Chemical 
Conditions  of  Plant  (irorcf/i,  319. — Condition  of  Plant-food  Ingredients, 
in  the  Soil,  319. — Water-soluble,  Reserve,  and  Insoluble  Part,  320.— 
Hydrous  or  "  Zeolitic  "  Silicates,  321. — Recognition  of  the  Prominent 
Chemical  Character  of  Soils,  322. — Aridity,  Neutrality  and  Alkalinity, 


xii  CONTENTS. 

322. — Chemical  Analysis,  323. — Water-Soluble  and  Acid-Soluble  Por- 
tions most  Important,  324. — We  cannot  Imitate  Plant-root  Action,  324 
Cultural  Experience  the  Final  Test,  324. — Analysis  of  Cultivated  Soils, 
325. — Methods  of  Analysis,  325.  —  The  Solvent  Action  of  Water  upon 
Soils,  327. — Extraction  of  Soils  with  Pure  Water,  327. — Continuous 
Solubility  of  Soil  Ingredients.  Tables,  328. — King's  Results.  Table, 
329. — Composition  and  Analysis  of  Janesville  Loam,  331. — Solubility  of 
Soil  Phosphates  in  Water,  332. — Practical  Conclusions  from  Water 
Extraction,  332. — Ascertainment  of  the  Immediate  Plant-food  Require- 
ments of  Cultivated  Soils  by  Physiological  Tests,  333.— Plot  Tests; 
their  uncertainties.  Diagram,  334. — Crop  Analysis  as  a  Test  of  Soil 
Character,  337. — Chemical  Tests  of  immediately  Available  Plant  Food  ; 
Dyer's  Method,  338. 

CHAPTER  XIX. 

ANALYSIS  OF  VIRGIN  SOILS  BY  EXTRACTION  WITH  STRONG  ACIDS  AND  ITS 
INTERPRETATION,  340.  — Loughridge's  Investigation  on  Strength  of  Acid 
and  Time  of  Digestion,  340. — Writer's  Method,  342. — Virgin  Soils  with 
High  Plant-food  Percentages  are  always  Productive.  Table,  343. — Dis- 
cussion of  Table,  343. — Low  Plant-food  Percentages  not  always  Indica- 
tion of  Sterility,  346. — What  are  "Adequate"  Percentages  of  Potash, 
Lime,  Phosphoric  Acid  and  Nitrogen,  347. — Soil-Dilution  Experiments, 
347. — Table  of  Compositions,  350. — Figures  of  Plants  and  their  Root- 
Development,  351. — Limitation  of  Root  Action,  351. — Lowest  Limits  of 
Plant-food  Percentages  and  Productiveness  Found  in  Virgin  Soils,  353. 
Limits  of  Adequacy  of  the  Several  Plant-food  Percentages  in  Virgin 
Soils,  353. — Lime  a  Dominant  Factor  in  Interpretation,  353. — Potash, 
354. — Phosphoric  Acid,  355. — Action  of  Lime  and  Ferric  Oxid,  355. — 
Table  of  Hawaiian  Ferruginous  Soils,  356. — Unavailability  of  Ferric 
Phosphate,  356. — Nitrogen,  357. — Nitrification  of  the  Organic  Matter 
of  the  Soil,  358. — Analysis  of  Soil  from  the  Ten-Acre  Tract  at  Chino, 
Cal.,  358. — Experiments  and  Results;  Matiere  Noire  the  Only  Guide, 
360. — What  are  Adequate  Nitrogen  Percentages  in  the  Humus  ?  360. — • 
Table  of  Humus  and  Nitrogen-Content  of  California!!  and  Hawaiian 
Soils,  361. — Confirmatory  Experiment.  Figure,  362. — Data  for  Nitrogen- 
Adequacy.  Table,  363. — Influence  of  Lime  upon  Soil  Fertility,  365. — 
"  A  Lime  Country  is  a  Rich  Country,"  365. — Effects  of  High  Lime-Con- 
tent in  Soils,  365. — Table  of  Soils  showing  Low  Phosphoric  Acid  with 
High  and  Low  Lime-Content,  366. — What  are  Adequate  Lime-percent- 
ages ?  Differ  for  Light  and  Heavy  Soils,  367. — Table  Showing  Need  of 
High  Lime  Percentages  in  Heavy  Clay  Soils,  368. — European  Standards 
for  Land  Estimates,  369. — Maercker's  Table,  369. 

CHAPTER  XX. 

SOILS  OF  THE  ARID  AND  HUMID  REGIONS,  371. — Composition  of  Good 
Medium  Soils  ;  Table,  371. — Criteria  of  Lands  of  the  Two  Regions,  371. 
— Tables  of  Soil-Composition  in  Both  Regions,  372. — Soils  of  the  Humid 
Region  governed  by  Time,  374. — Soils  of  the  Arid  Region  Governed 


CONTENTS.  xiii 

by  Moisture,  374. — Lime  and  Magnesia  Uniformly  High  in  Arid  Soils, 
Despite  Scarcity  of  Limestone  Formations  ;  Potash  also  High,  374. — 
General  Comparison  of  the  Soils  of  the  Arid  and  Temperate  Humid 
Regions,  375. — Basis  of  Same,  376. — New  Mexico  and  Analysis  of  Soil, 
376. — General  Table,  377. — Discussion  of  the  Table,  sj8.—Liwe  ;  Sum- 
mary of  Physical  and  Chemical  Effects  of  Lime  Carbonate  in  Soils,  378. 
Discussion  of  Summary,  379. — Magnesia  :  Its  role  in  Plant  Nutrition, 
381. — Manganese:  Its  Stimulant  Action,  383. —  The  "Insoluble  tfes- 
idue"or  Silicates,  384. — Soluble  Silica  and  Alumina,  384. — Analysis 
of  Clay  from  Soil,  385. — Difference  in  Sand  of  Arid  and  Humid  Regions. 
Table,  386. — Soluble  Silica  or  Hydrous  Silicates  more  Abundant  in  Arid 
than  in  Humid  Soils,  388. — Aluminic  Hydrate.  Table.  389. — Retention 
of  Soluble  Silica  in  Alkali  Soils,  391. — Ferric  Hydrate,  392. — Phosphoric 
Acid,  392. — Sulftiric  Acid,  394. — Potash  and  Soda,  Retained  more  in 
Arid  Soils,  394. — Arid  Soils  Rich  in  Potash,  395.— Humus,  Low  in  Arid 
Soils,  but  Rich  in  Nitrogen,  396. — The  Transition  Region,  397. 

CHAPTER  XXL 

SOILS  OF  ARID  AND  HUMID  REGIONS  CONTINUED,  398. — Soils  of  the  Tropics, 
398. — Humus  in  Tropical  Soils,  399. — Investigations  of  Tropical  Soils, 
401. — Soils  of  Samoa  and  Kamerun,  402. — Soils  of  the  Samoan  Islands, 
403. — Soils  of  Kamerun,  404. — Soils  of  Madagascar,  405. — Soils  of 
India,  410. — The  Indo-Gangetic  Plain,  411. — The  Brahmaputra  Al- 
luvium in  Assam,  413. — Black  Soils  of  Deccan,  414. — Red  Soils  of  the 
Madras  Region,  415. — Laterite  Soils,  416. — Influence  of  Aridity  upon 
Civilization,  417. — Preference  of  Ancient  Civilizations  for  Arid  Coun- 
tries, 417. — Irrigation  Necessitates  Co-operation,  419. — High  and  Per- 
manent Productiveness  of  Arid  Soils  Induces  Permanence  of  Civil 
Organization,  419. 

CHAPTER  XXII. 

ALKALI  SOILS,  THEIR  NATURE  AND  COMPOSITION,  422. — Alkali  Lands  z>s. 
Seashore  Lands,  422. — Origin,  422. — Deficient  Rainfall,  423. — Predom- 
inant vSalts,  423. — Geographical  Distribution,  424. — Their  Utilization  of 
World-wide  Importance,  424.  —  Repellent  Aspect,  Plate,  424.  —  Effects  of 
Alkali  upon  Culture  Plants.  Figures  of  Apricot  Trees,  426. — Nature  of 
the  Injury,  External  and  Internal,  426. —  Effects  of  Irrigation,  428. — 
Leaky  Irrigation  Ditches,  429. — Surface  and  Substrata  of  Alkali  Lands, 
429 — Vertical  Distribution  of  the  Salts  in  Alkali  Soils,  429.  —  How 
Native  Plants  Live,  430.  —  Figures  of  various  Phases  of  Reclamation, 
431.  —  Upward  Translocation  from  Irrigation,  433.  —  Distribution  of  Al- 
kali in  Sandy  Lands,  433.  In  Heavier  Lauds,  436.— Salton  Basin  or 
Colorado  Delta,  436. — Diagram  of  Alkali  Distribution  in  Same,  438. — 
Horizontal  Distribution  of  Alkali  Salts  in  Arid  Lands,  439.  — Alkali  in 
Hill  Lands,  439.  — Usar  Lands  of  India,  440. — "  S/.ek  "  Lands  of  Hungary, 
440. —Alkali  Lands  of  Turkestan,  441.  —  Composition  and  Quantity  <-f 
Salts  Present,  441.— Nutritive  Salts,  441.  — Black  and  White  Alknli. 
Tables,  442.  — Estimation  of  Total  Alkali  in  Land,  ^.—Composition  oj 


xiv  CONTENTS. 

Alkali  Soils  as  a  whole.  Tables,  445. — Presence  of  much  Carbonate  of 
Soda,  448. — Cross  Section  of  an  Alkali  Spot.  Table,  448. — Reactions 
between  the  Carbonates  and  Sulfates  of  Earths  and  Alkalies.  Figure  of 
Curve,  449. — Inverse  Ratios  of  Alkali  Sulfates  and  Carbonates.  Dia- 
grams, 451. — Exceptional  Conditions,  453. — Summary  of  Conclusions, 
453- 

CHAPTER  XXIII. 

UTILIZATION  AND  RECLAMATION  OP  ALKALI  LAND,  455. — Alkali-resistant 
Crops,  455. — Counteracting  Evaporation,  455. — Turning-under  of  Sur- 
face Alkali,  456. — Shading,  457. — Neutralizing  Black  Alkali,  457. — 
Removing  the  Salts  from  the  Soils,  458. — Scraping  off,  458. — Teaching- 
Down.  Figure,  459. — Underdrainage,  the  Final  and  Universal  Remedy 
for  Alkali,  460. — Possible  Injury  to  Land  by  Excessive  Leaching,  462. 
— Difficulty  in  Draining  "  Black  "  Alkali  Land,  462. — Swamping  of  Al- 
kali Land,  463. — Removal  of  Alkali  Salts  by  Certain  Crops,  463. — 
Tolerance  of  Alkali  by  Culture  Plants,  463. — Relative  Injuriousness  of 
the  several  Salts.  Effects  on  Sugar  Beets,  464. — Table  of  Tolerances  ; 
Comments  on  same,  467. — Saltbushes  and  Native  Grasses.  Australian 
Saltbushes,  469. — Modiola  ;  Native  and  Cultivated  Grasses,  469. — Other 
Herbaceous  Crops,  472. — Legumes,  472. — Mustard  Family,  473. — Sun- 
flower Family,  473. — Root  Crops,  474. — Stem  Crops,  475. — Textile  Plants, 
475. — Shrubs  and  Trees,  475. — Vine,  Olive,  Date,  Citrus  Trees.  Deci- 
duous Orchard  Trees.  Timber  and  Shade  Trees,  475. — Inducements 
toward  the  Reclamation  of  Alkali  Lands,  481. — Wheat  on  Reclaimed 
Land  at  Tulare  ;  Figure,  482. — Need  of  Constant  Vigilance,  484. 

CHAPTER  XXIV. 

THE  RECOGNITION  OF  SOIL  CHARACTER  FROM  THE  NATIVE  VEGETATION  ; 
MISSISSIPPI,  487.— Climatic  and  Soil  Conditions,  487. — Natural  Vegeta- 
tion the  Basis  of  Land  Values  in  the  United  States,  488. — Investigation 
of  Causes  Governing  Distribution  of  Native  Vegetation,  488. — Investiga- 
tions in  Mississippi,  489. — Vegetative  Belts  in  Northern  Mississippi, 
490. — Sketch  Map  of  Same,  with  Tabulation  of  Lime  Content  and 
Native  Vegetation,  490. — Lime  Apparently  a  Governing  Factor,  492. — 
Soil  Belts  in  Southern  Mississippi,  493. — Vegetative  and  Soil  Features 
of  Coast  Belts.  Diagram,  495. — Table  of  Plant-Food  percentages  and 
Native  Growth,  496. — Definition  of  Calcareous  Soils,  496. — Differences 
in  the  Form  and  Development  of  Trees,  498. — Forms  of  the  Post  Oak. 
Figures,  498. — Forms  of  the  Black  Jack  Oak.  Figures,  500. — Charac- 
teristic Forms  of  other  Oaks,  502. — Sturdy  Growth  on  Calcareous  Lands, 
502. — Growth  of  Cotton,  503. — Lime  Favors  Fruiting,  and  compact 
Growth,  504. — Physical  vs.  Chemical  Causes  of  Vegetative  Features, 
505. — Lowland  Tree  Growth,  506. — Contrast  between"  First"  and 
"Second"  Bottoms,  506.— Tree  Growth  of  the  First  Bottoms.  The 
Cypress,  507. — Figures  of  Swamp  and  Upland  Cypress,  508. — Other 
Lowland  Trees,  509. — General  Forecasts  of  Soil  Quality  in  Forest  Lands, 
509- 


CONTENTS.  xv 

CHAPTER  XXV. 

RECOGNITION  OF  THE  CHARACTER  OF  SOILS  FROM  THEIR  NATIVE  VEGE- 
TATION. UNITED  STATES  AT  LARGE,  EUROPE,  511.— Forest  Growths 
outside  of  Mississippi  ;  Alabama,  Louisiana,  Western  Tennessee,  and 
Western  Kentucky,  511. — North  Central  States  East  of  the  Mississippi 
River,  513. — Upland  and  Lowland  Vegetation  in  the  Arid  and  Humid 
Region,  515. — Forms  of  Deciduous  Trees  in  the  Arid  Region,  516. — 
Tall  Growth  of  Conifers,  517. — Herbaceous  Plants  as  Soil  Indicators, 
517. — Leguminous  Plants  Usually  Indicate  Rich  or  Calcareous  Lands, 
518. — European  Observations  and  Views  on  Plant  Distribution  and  its 
Controlling  Causes,  519. — Composition  of  Pine  Ashes  on  Calcareous  and 
Non-calcareous  Lands.  Table,  52o.--Calciphile,  Calcifuge,  and  Indifferent 
Plants,  521. — Silicophile  vs.  Calciphile  Flora,  523. — What  is  a  Calcareous 
Soil  ?  524. — Predominance  of  Calcareous  Formations  in  Europe,  525. 

CHAPTER  XXVI. 

THE  VEGETATION  OF  SALINE  AND  ALKALI  LANDS,  527. — Marine  Saline 
Lands,  527. — General  Character  of  Saline  Vegetation,  527. — Structural 
and  Functional  Differences  Caused  by  Saline  Solutions,  528. — Absorp- 
tion of  the  Salts.  Table,  529. — Injury  from  the  Various  Salts,  531. — 
Reclamation  of  Marine  Saline  Lands  for  Culture,  533. —  The  Vegetation 
of  Alkali  Lands,  534. — Reclaimable  and  Irreclaimable  Alkali  Lands 
as  Distinguished  by  their  Natural  Vegetation,  534. — Plants  Indicating 
Irreclaimable  Lands,  535. — Tussock  Grass  ;  Bushy  Samphire  ;  Dwarf 
Samphire  ;  Saltwort  ;  Greasewood  ;  Alkali  Heath  ;  Cressa  ;  Salt  Grass, 
536. — Relative  Tolerances  of  the  different  Species  ;  Table,  549. 


APPENDICES. 

A. — Directions  for  taking  Soil  Samples,  issued  by  the  California  Experiment 

Station,  553. 

B. — Summary  Directions  for  Soil-Examination  in  the  Field  or  Farm,  556. 
C. — Short  Approximate  Methods  of  Chemical  Soil-Examination  Used  at  the 

California  Experiment  Station,  560. 
General  Index,  565. 
Index  of  Authors  referred  to,  591. 


PREFACE. 

THIS  volume  was  originally  designed  to  serve  as  a  text- 
and  reference  book  for  the  students  attending  the  writer's 
course  on  soils,  given  annually  at  the  University  of  California, 
who  complained  of  their  inability  to  find  in  any  connected  treat- 
ise a  large  portion  of  the  subject  matter  brought  before  them. 
As  all  these  students  harl  preliminary  training  in  physics,  chem- 
istry and  botany,  no  introductory  chapters  on  these  general 
subjects  were  necessary  or  contemplated ;  the  more  so  as  good 
elementary  treatises  embracing  the  needful  preparation  are 
now  numerous. 

As  time  progressed,  however,  outside  demands  for  a  book 
embodying  the  writer's  soil  studies  in  the  humid  and  arid 
regions,  especially  the  latter,  became  so  numerous  and  pressing 
that  the  scope  of  the  work  has  gradually  been  much  enlarged 
to  conform  to  these  demands ;  and  this,  rather  than  com- 
pleteness of  detail,  when  such  detail  can  be  found  well  given 
elsewhere,  has  been  the  guide  in  the  necessary  condensa- 
tion of  the  whole.  To  give  the  entire  subject  matter  full  eluci- 
dation, would  require  several  more  volumes. 

It  may  not  be  unnecessary  to  explain  at  the  outset  why  and 
how  this  treatise  deviates  in  many  respects  from  previous  pub- 
lications on  the  same  general  topic.  From  boyhood  up  it  has 
fallen  to  the  writer's  lot  to  be  almost  continuously  in  more  or 
less  direct  contact  with  the  conditions  and  requirements  of 
newly  settled  regions,  as  well  as  with  those  hardly  yet  invaded 
even  by  the  pioneer  farmer;  where  the  question  of  cultural 
adaptation  was  yet  undetermined  or  wholly  in  the  dark.  Being 
during  his  active  life  constantly  called  upon  in  his  official  capa- 
city to  give  information  and  advice  to  pioneer  farmers  or  in- 
tending settlers  in  regard  to  the  merits  and  adaptations  of  virgin 
soils,  the  writer's  attention  was  naturally  and  forcibly  directed 
toward  soil  investigation  as  a  possible  means  of  determining, 
beforehand,  the  general  prospects  and  special  features  of  agri- 


xviii  PREFACE. 

culture  in  regions  where  actual  experience  was  either  non-exis- 
tent or  very  brief  and  partial.  In  the  pursuit  of  these  studies 
he  has  been  favored  by  exceptional  opportunities,  extending 
over  a  varied  climatic  area  reaching  on  the  south  from  the  Gulf 
of  Mexico  to  the  Ohio,  across  to  the  Pacific  coast,  and  to 
British  Columbia  on  the  north.  That  a  systematic  investiga- 
tion of  soils  over  so  large  an  area,  covering  both  humid  and 
arid  regions,  should  lead  to  some  unexpected  and  novel  re- 
sults, is  but  natural ;  and  it  is  the  discussion  of  these  results  in 
connection  with  those  obtained  elsewhere,  and  with  some  of 
the  prevailing  views  based  thereon,  that  must  serve  as  the 
justification  for  the  present  addition  to  an  already  well- 
stocked  branch  of  literature. 

From  the  very  beginning  of  the  scientific  study  of  agricul- 
ture, the  investigation  of  soils  with  a  view  to  the  a  priori  de- 
termination of  their  adaptation,  permanent  value,  and  best 
means  of  cultural  improvement,  has  formed  the  subject  of 
continuous  effort.  It  is  not  easy  to  imagine  a  subject  of 
higher  direct  importance  to  the  physical  welfare  of  mankind, 
whose  very  existence  depends  on  the  yearly  returns  drawn  by 
cultural  labor  from  the  soil. 

It  is  certainly  remarkable  that  after  all  this  long-continued 
effort,  even  the  fundamental  principles,  and  still  more  the 
methods  by  which  the  object  in  view  is  to  be  attained,  are 
still  so  far  in  dispute  that  a  unification  of  opinion  in  this  re- 
spect is  not  yet  in  view ;  and  a  return  to  pure  empiricism  is  from 
time  to  time  brought  forward  to  cut  the  Gordian  knot. 

While  this  state  of  things  is  primarily  due  to  the  intrinsic 
complexity  and  difficulty  of  the  subject  itself,  it  has  unquestion- 
ably been  materially  aggravated  by  accidental,  partly  historic 
conditions.  Foremost  among  these  is  the  fact  that  until  within 
recent  times,  soil  studies  have  borne  almost  entirely  on  lands 
long  cultivated  and  in  most  cases  fertilized :  thus  changing 
them  from  their  natural  condition  to  a  more  or  less  artificial 
one,  which  obscures  the  natural  relations  of  each  soil  to  vege- 
tation. 

The  importance  of  these  relations  is  obvious,  both  from  the 
theoretical  and  from  the  practical  standpoint.  From  the 
former,  it  is  clear  that  the  native  vegetation  represents,  within 
the  climatic  limits  of  the  regional  flora,  the  result  of  a  secular 


PREFACE.  xix 

process  of  adaptation  of  plants  to  climates  and  soils,  by  nat- 
ural selection  and  the  survival  of  the  fittest.  The  natural 
floras  and  sylvas  are  thus  the  expression  of  secular,  or  rather, 
millennial  experience,  which  if  rightly  interpreted  must  convey 
to  the  cultivator  of  the  soil  the  same  information  that  other- 
wise he  must  acquire  by  long  and  costly  personal  experience. 

The  general  correctness  of  this  axiom  is  almost  self-evi- 
dent ;  it  is  explicitly  recognized  in  the  universal  practice  of 
settlers  in  new  regions,  of  selecting  lands  in  accordance  with 
the  character  of  the  forest  growth  thereon;  it  is  even  legally 
recognized  by  the  valuation  of  lands  upon  the  same  basis,  for 
purposes  of  assessment,  as  is  practiced  in  a  number  of  States. 

The  accuracy  with  which  experienced  farmers  judge  of  the 
quality  of  timbered  lands  by  their  forest  growth,  has  justly 
excited  the  wonder  and  envy  of  agricultural  investigators, 
whose  researches,  based  upon  incomplete  theoretical  assump- 
tions, failed  to  convey  to  them  any  such  practical  insight.  It 
was  doubtless  this  state  of  the  case  that  led  a  distinguished 
writer  on  agriculture  to  remark,  nearly  half  a  century  ago, 
that  he  "  would  rather  trust  an  old  farmer  for  his  judgment 
of  land  than  the  best  chemist  alive/'  l 

It  is  certainly  true  that  mere  physico-chemical  analyses,  un- 
assisted by  other  data,  will  frequently  lead  to  a  wholly  errone- 
ous estimate  of  a  soil's  agricultural  value,  when  applied  to  cul- 
tivated lands.  But  the  matter  assumes  a  very  different  as- 
pect when,  with  the  natural  vegetation  and  the  corresponding 
cultural  experience  as  guides,  we  seek  for  the  factors  upon 
which  the  observed  natural  selection  of  plants  depends,  by 
the  physical  and  chemical  examination  of  the  respective  soils. 
It  is  further  obvious  that,  these  factors  being  once  known, 
we  shall  be  justified  in  applying  them  to  those  cases  in  which 
the  guiding  mark  of  native  vegetation  is  absent,  as  the  result 
of  causes  that  have  not  materially  altered  the  natural  condition 
of  the  soil. 

It  is  probable  that,  had  agricultural  science  been  first  de- 
veloped in  regions  where  the  external  conditions  permitted 
the  carrying-out  of  such  a  course  of  investigation,  instead  of 
in  the  abnormally  temperate,  even  and  humid  climate  of  middle 

1  "  The  Soil  Analyses  of  the  Geological   Surveys   of   Kentucky  and   Arkansas." 
S.  W.  Johnson  in  AM.  JOUR.  SCI.,  Sept.  1861. 


xx  PREFACE. 

Europe,  with  its  long-cropped,  worn  fields,  and  very  predomi- 
nantly calcareous  soils,  the  present  condition  of  this  science 
might  differ  not  immaterially  from  that  actually  existing.  As 
a  matter  of  fact,  it  has  attained  its  present  state  under  very 
disadvantageous  external  conditions,  which  frequently  necessi- 
tated a  recourse  to  highly  complex  and  laborious  methods  and 
artificial  appliances,  for  the  establishment  and  maintenance 
of  the  conditions  which  elsewhere  might  have  been  found 
abundantly  realized  in  nature;  thus  permitting,  by  the  multi- 
plication of  observations  over  extended  and  widely  varied  areas, 
the  elimination  and  control  of  accidental  errors  of  experiment 
and  observation. 

Just  as  in  historical  geology  the  subdivisions  of  formations 
observed  and  accepted  in  Europe  formed  for  many  years  a  pro- 
crustean  bed  upon  which  the  facts  observed  elsewhere  had  to 
be  stretched,  so  in  the  domain  of  soil  physics  and  chemistry, 
and  even  in  vegetable  physiology,  the  observations  made  in  the 
really  exceptional  climates  and  soils  of  middle  Western 
Europe,  have  often  erroneously  been  construed  as  constituting 
a  general  basis  for  unalterable  deductions. 

The  rapid  extension  of  civilization  and  the  carrying  of 
minute  scientific  research  into  other  regions,  now  rendered 
possible  by  the  improved  means  of  communication,  has  shown 
the  one-sidedness  of  some  of  the  views  prevailing  heretofore, 
inasmuch  as  they  are  really  applicable  only  to  accidental  and 
rather  exceptional  conditions. 

It  is  therefore  one  object  of  this  volume  to  present  and 
discuss  summarily  the  facts  of  physical  and  chemical  soil  con- 
stitution and  functions  with  reference  to  the  additional  light 
afforded  on  the  wider  basis,  embracing  both  the  humid  and  the 
arid  regions ;  of  which  the  latter  has,  as  such,  received  but  scant 
and  desultory  attention  thus  far,  to  the  detriment  of  both  the 
work  of  the  agricultural  experiment  stations  and  of  agricul- 
tural practice.  The  book  therefore  includes  the  discussion 
both  of  the  methods  and  results  of  direct  physical,  chemical  and 
botanical  soil  investigation,  as  well  as  the  subject  matter  relat- 
ing to  the  origin,  formation,  classification  and  physical  as  well 
as  chemical  nature  of  soil,  usually  included  in  works  on  scien- 
tific agriculture. 

In  the  presentation  of  these  subjects,  it  has  been  the  writer's 


PREFACE.  xxi 

aim  to  reach  both  the  students  in  his  own  classes  and  in  the 
agricultural  colleges  generally,  as  well  as  the  fast  increasing 
class  of  farmers  of  both  regions  who  are  willing  and  even 
anxious  to  avail  themselves  of  the  results  and  principles  of 
scientific  investigation,  without  "  shying  off  "  from  the  new 
or  unfamiliar  words  necessary  to  embody  new  ideas.  It 
would  seem  to  be  time  that  the  latter  class,  and  more  especially 
those  constituting  farmers'  clubs,  should  learn  to  understand 
and  appreciate  both  the  terms  and  methods  of  scientific  reason- 
ing, which  are  likely  to  form,  increasingly,  the  subjects  of  in- 
struction in  the  public  schools.  But  in  order  to  segregate  to 
some  extent  the  generally  intelligible  matter  from  that  which 
requires  more  scientific  preparation  than  can  now  be  generally 
expected,  it  has  been  thought  best  to  use  in  the  text  two  kinds 
of  type ;  the  larger  one  embodying  the  matter  presumed  to  be 
interesting  and  intelligible  to  the  general  reader,  while  the 
smaller  type  carries  the  illustrative  detail  and  discussion  which 
will  be  sought  chiefly  by  the  student. 

As  regards  the  chemical  nomenclature  used  in  this  volume, 
the  writer  has  not  thought  it  advisable  to  follow  the  example 
set  by  some  late  authors  in  substituting  for  the  well-known 
names  of  the  bases  and  acids,  those  of  the  elements,  and  still 
less,  those  of  the  intangible  ions.  Any  one  who  has  taught 
classes  in  agricultural  chemistry  will  have  experienced  the 
difficulty  and  loss  of  time  unnecessarily  incurred  in  the  inces- 
santly recurring  transposition  of  terms,  and  complication  of 
formulae,  serving  no  useful  purpose  save  that  of  academic  con- 
sistency. It  is  of  at  least  doubtful  utility  to  present  to  the 
farmer,  c.  g.,  the  inflammable  and  dangerous  elements  phos- 
phorus and  potassium  as  prime  factors  in  the  success  of  his 
crops,  and  of  healthy  nutrition. 

Inasmuch  as  all  the  elements  are  presented  to  and  con- 
tained in  the  plant  in  compounds  only,  and  these  compounds  are 
themselves,  in  the  dilute  solutions  used  by  plants,  known  to  be 
largely  dissociated  into  their  basic  and  acid  groups,  it  seems  to 
be  most  natural  to  present  them  under  the  corresponding,  even 
if  not  absolutely  theoretically  correct  names  of  acids  and  bases, 
to  which  the  farmer  and  the  trade  have  been  accustomed  for 
half  a  century.  Upon  these  considerations  the  long-used 
designations  of  potash,  soda,  lime,  phosphoric,  sulfuric,  nitric 


xxii  PREFACE. 

and  other  acids  and  bases  have  been  retained  in  this  volume, 
adding  the  chemical  formula  where,  as  in  analytical  statements, 
a  doubt  as  to  their  meaning  might  arise.  Assuredly,  the  diffu- 
sion of  scientific  knowledge  should  not  be  needlessly  hindered 
by  the  adoption  of  a  pedantic  mode  of  presentation. 

The  great  breadth  of  the  subject  of  this  volume  has  ren- 
dered inadvisable  any  extended  bibliography,  such  as  it  has  of 
late  become  customary  to  add  to  works  of  this  kind.  References 
have  therefore  been  restricted  to  publications  specially  discussed, 
and  to  such  as  are  not  widely  known  on  account  of  limited 
circulation. 

The  author's  warmest  acknowledgments  are  due  to  Professor 
R.  H.  Loughridge,  of  the  University  of  California,  for  effi- 
cient and  sympathetic  assistance,  both  in  the  revision  of  the 
manuscript,  and  active  personal  help  in  the  preparation  of  the 
illustrations.  Without  his  cooperation  the  preparation  and 
publication  of  the  volume  would  have  been  much  longer  de- 
layed. 

Acknowledgments  are  also  due  for  helpful  suggestions  and 
criticism  to  Professors  L.  H.  Bailey,  of  Cornell  University, 
F.'  H.  King,  of  Wisconsin,  and  Jacques  Loeb  of  the  University 
of  California. 

E.  W.  HILGARD. 

BERKELEY,  CALIFORNIA, 
JVovember  15,  1905. 


INTRODUCTION. 

Definition  of  Soils. — In  the  most  general  meaning  of  the 
term,  a  soil  is  the  more  or  less  loose  and  friable  material  in 
which,  by  means  of  their  roots,  plants  may  or  do  find  a  foot- 
hold and  nourishment,  as  well  as  other  conditions  of  growth. 
Soils  form  the  uppermost  layer  of  the  earth's  crust ;  but  the 
term  does  not  indicate  any  such  definite  average  texture  as  is 
sometimes  implied  by  its  popular  use  to  designate  certain  loose, 
loamy  materials  found  in  older  geological  formations.  We  do 
find  in  these,  not  unfrequently,  layers  that  in  the  past  have 
served  to  support  vegetation,  as  evidenced  by  remains  of  plants 
found  therein.  But  as  a  rule,  such  ancient  soils  are  much 
compacted  and  otherwise  changed,  and  would  not  now  be 
capable  of  performing  the  office  of  plant  nutrition  without 
previous,  long-continued  exposure  to  the  same  agencies  by 
which  all  soils  were  originally  formed  from  pre-existing  rocks. 
Within  the  latter  category  must  be  included,  in  scientific  par- 
lance, not  only  the  hard  rocks  known  as  such  in  daily  life,  but 
also  such  soft  materials  as  clay,  sand,  marls,  etc.,  which  often 
compose,  partially  or  wholly,  the  bodies  of  wide-spread  geo- 
logical formations. 

Elements  Constituting  the  Earth's  Crust. — More  than 
seventy  elementary  substances  have  been  found  within  the 
portion  of  the  earth  accessible  to  man ;  most  of  these  are  present 
only  in  very  minute  proportions  ;  of  those  occurring  in  relatively 
considerable  quantities,  a  list  showing  their  approximate  pro- 
portions is  given  below. 

Average  quantitative  composition  of  the  EartJi's  Crust.— 
The  total  thickness  of  the  outer  shell  of  the  earth,  thus  far 
known  to  us,  does  not  exceed  about  95.000  feet,  as  observed 
in  the  accessible  rock  deposits.  Estimates  of  the  proportions 
in  which  the  more  abundant  elements  contribute  to  the  com- 
position of  these  constituent  rocks,  have  repeatedly  been  made. 
The  latest  and  most  widely  accepted  of  these,  by  F.  W.  Clarke, 
of  the  U.  S.  Geological  Survey,  is  given  herewith.  It  in- 


8«.7Q 

Silicon          

27  .21 

Aluminum  

7.8l 

'        , 

c.46 

Calcium  

7.77 

o.o<c 

Magnesium  

,  2.68 

0.  14. 

Sodium           .  .        

Z.-& 

I  .  14. 

Potassium     .          

2  .  40 

o  04 

Hydrogen  

0.  21 

10.67 

Carbon  

O    22 

O.OO2 

Chlorin  

O.OI 

2.  07 

Phosphorus  

......                 O.  IO 

Manganese  

,  0.08 

Sulphur  .      .  .        

O.OT 

o  09 

Barium  

O.O"? 

Fluorin  

O.O2 

Chromium  .  . 

O.OI 

xxiv  INTRODUCTION. 

eludes  the  constituents  of  the  sea  and  atmosphere  as  well; 
these  two  constitute  about  7  per  cent  of  the  whole,  93  per  cent 
being  solid  rocks. 

RELATIVE  ABUNDANCE  OF  THE  ELEMENTS  TO  A  DEPTH  OF  TEN  KILOMETERS 

SOLID  CRUST  OCEAN  MEAN, 

(93  PER  CENT).  (7  PER  CENT).  INCLUDING  AIR. 

49.98 

25-30 
7.26 
5-o8 

3-5* 
2.50 
2.28 
2.23 
0.94 
0.30 

O.2I 
O.IS 

0.09 
0.07 
O.O4 
0.03 
O.O2 
O.O2 
0.01 

It  will  be  noted  that  one-half  of  the  total  consists  of  oxygen, 
and  that  nearly  86%  (or  47.29%  of  the  49.98%)  of  this 
amount  is  contained  in  the  solid  rocks;  nearly  2.50%  of  the 
remainder  in  sea  and  other  water;  and  .41%  in  the  atmosphere, 
in  the  free  condition,  in  which  it  serves  for  the  respiration  of 
animals  and  plants,  and  for  the  various  processes  of  slow  and 
rapid  combustion,  or  "  oxidation."  This  relatively  small  pro- 
portion of  the  whole,  is,  nevertheless,  the  most  directly  im- 
portant for  the  maintenance  of  organic  life. 

Oxids  Constitute  Earth's  Crust. — The  vast  predominance 
of  oxygen  in  the  above  list  suggests  at  once  that  most  of  the 
other  elements  must  exist  in  combination  with  it,  i.  e.,  as 
"  oxids."  H.  S.  Washington  x  has  lately  revised  the  esti- 
mates heretofore  made,  on  the  basis  of  a  very  large  number  of 
analyses  made  by  him  and  others,  of  rocks  within  the  United 
States,  and  gives  the  following  table;  alongside  of  which  is 
placed  a  revised  estimate  by  Clarke,  which  also  includes  rocks 
from  abroad;  both  being  given  in  terms  of  oxids  of  the  several 
elements. 

1  U.  S.  Geol.  Survey,  Professional  Paper  No.  14,  p.  108. 


INTRODUCTION.  xxv 

WASHINGTON.     CLARKE. 

Silica SiO.  57-?8  59-§9 

Alumina Al.,0,  15.67  15.45 

Peroxid  of  Iron Fe2Og  3.31  2.64 

Protoxid  of  Iron FeO  3.84  3.53 

Magnesia MgO  3.81  4.37 

Lime CaO  5.18  4.91 

Soda Na2Oi  3.88  3.56 

Potash K2O  3.13  2.81 

Water,  basic H2O-f-  1.42  1.52 

Water,  acid H  2O —  .36  .40 

Ferric   Sulphid FeSg  1.03  .60 

Phosphoric  acid PsOs  .37  .22 

Manganese  Protoxid MnO  .22  .10 

The  salient  point  which  at  once  attracts  attention  in  these 
tables  is  the  great  predominance  of  the  oxid  of  silicon — silica, 
silicic  acid,  quartz,  etc., — over  all  other  substances.  While 
quartz  occurs  alone  in  enormous  masses,  as  will  be  shown 
later,  probably  the  greater  proportion  is  found  in  combina- 
tion with  other  oxids,  notably  those  of  aluminum,  calcium, 
iron,  magnesium,  and  the  alkali  metals  potassium  and  sodium. 
Chlorin  and  fluorin,  however,  do  not  occur  as  oxids.1 

The  Chemical  Elements  Important  to  Agriculture. — Of  the 
numerous  elements  known  to  chemists,  only  eighteen  require 
mention  in  connection  with  either  soil  formation  or  plant 
growth ;  and  of  these  only  thirteen  or  fourteen  participate  in 
normal  plant  growth.  They  are  the  following: 

METALLIC    ELEMENTS.  NON-METALLIC    ELEMENTS. 

Potassium  Carbon 

Sodium  Hydrogen 

Calcium  Oxygen 

Magnesium  Nitrogen 

Iron  Phosphorus 

Manganese  Sulphur 

Aluminum  Chlorin 

Titanium  Fluorin 

lodin 
Silicon. 

Of  this  list,  titanium,  though  a  very  constant  ingredient  of 

1  A  trifling  amount  of  chlorin  is  found  oxidized  in  the  form  of  sodium  perchlor- 
ate,  in  the  nitre  deposits  of  Chile. 


xxvi  INTRODUCTION. 

soils  in  the  form  of  titanic  dioxid,  is  not  known  as  performing 
any  important  function  in  soils,  and  is  not,  so  far  as  known 
at  present,  ever  taken  up  by  plants.  Aluminum,  in  the  form 
of  its  compounds  with  oxygen  and  silicon,  is  a  very  prominent 
and  physically  very  important  soil  ingredient,  but  does  not, 
apparently,  perform  any  direct  function  in  plant  nutrition,  and 
is  absent  from  their  ash,  except  in  the  case  of  some  of  the 
lower  plants  (horsetails  and  ferns). 

lodin  appears  to  be  normally  present  in  all  seaweeds,  and 
occurs  in  traces  in  some  land  plants.  Fluorin  is  a  normal  in- 
gredient of  animal  bones,  and  its  presence  in  plant  ashes  is 
often  easily  shown.  The  remaining  fourteen,  however,  are 
always  present  in  plants ;  carbon,  hydrogen,  oxygen  and  nitro- 
gen forming  the  volatile  or  combustible  part,  while  the  rest 
occur  in  the  ashes. 

It  is  true  that  other  elements,  or  rather  their  compounds,  are 
sometimes  found  in  plants,  being  taken  up  by  them  from  solu- 
tions existing  in  the  soil.  Thus  the  alkalies  caesium  and  rubi- 
dium, also  barium,  strontium,  zinc,  copper,  boron  and  some 
others,  may  be  absorbed  when  present  in  soluble  form.  But 
they  are  neither  necessary  nor  beneficial  to  plant  economy,  and 
when  in  considerable  amounts  are  harmful.  Thus  fifteen  ele- 
ments, ommiting  iodin  and  titanium,  alone  require  discussion. 

The  Volatile  Part  of  Plants,  as  already  stated,  consists 
of  carbon,  hydrogen,  oxygen  and  nitrogen.  Of  these,  car- 
bon is  obtained  by  the  plant  exclusively  from  the  carbonic 
(dioxid)  gas  of  the  air;  hydrogen  and  oxygen,  from  the  soil 
in  the  form  of  water;  nitrogen,  directly  from  the  soil  but  in- 
directly also  from  the  air,  through  the  agency  of  certain 
bacteria.  The  ash  ingredients  of  course  are  all  derived  from 
the  soil  through  the  roots,  and  must  all  be  present  in  the  lat- 
ter in  an  available  form,  to  a  sufficient  extent  to  supply  the 
demands  of  vegetation. 

The  Agencies  of  Soil  Formation. — With  respect  to  their 
mode  of  formation,  soils  may  be  defined  as  the  residual  product 
of  the  physical  disintegration  and  chemical  decomposition  of 
rocks ;  with,  ordinarily,  a  small  proportion  of  the  remnants  of 
organic  life.  The  agencies  producing  these  changes  are  those 
classed  under  the  general  term  "  atmospheric  "  or  "  meteoro- 


INTRODUCTION.  xxvh 

logical ;  "  they  include  therefore  the  action  of  temperature — 
heat  and  cold — that  of  water,  and  that  of  air  and  its  ingre- 
dients. In  popular  parlance,  it  includes  the  processes  of 
weathering;  nearly  the  same  processes  are  involved  in  the 
4t  fallowing  "  of  soils. 


PART  I. 

THE  ORIGIN  AND  FORMATION  OF  SOILS- 


CHAPTER  I. 

THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION. 

SINCE  the  physical  and  mechanical  effects  of  the  agencies 
mentioned  above  usually  precede,  in  time,  the  chemical  changes, 
which  are  materially  facilitated  by  the  previous  pulverization  of 
the  rocks,  the  former  should  be  first  considered. 

Effects  of  Iicat  and  cold  on  rocks. — Most  rocks  are  aggre- 
gates of  several  simple  minerals;  a  few  only  (limestone, 
quartzite  and  a  few  others)  expand  or  contract  alike  in  all  their 
parts.  Of  the  minerals  composing  the  compound  rocks, 
scarcely  any  expand  to  exactly  the  same  extent  under  the  in- 
fluence of  the  sun's  heat,  especially  when  their  colors  differ; 
nor,  in  the  great  majority  of  cases,  does  one  and  the  same 
mineral  expand  alike  in  all  three  directions.  It  follows  that  at 
each  change  of  temperature  there  is  a  tendency  to  the  forma- 
tion of  minute  fissures  between  adjacent  crystals  or  masses  of 
different  simple  minerals;  and  especially  in  the  case  of  large 
crystals  of  certain  kinds,  this  action  alone  will  gradually  result 
in  the  disruption  of  the  rock  surf  rice,  so  that  individual  crystals 
may  l)e  detached  with  little  difficulty.  In  any  case,  the  cracks  so 
formed  are  gradually  widened  by  a  frequent  repetition  of  the 
changes  of  temperature,  coupled  \vi1i  access  of  air.  water,  dust, 
and  the  rootlets  of  plants;  all  of  which  brings  about  a  gradu- 
ally increasing  rate  of  surface  crumbling.  This  is  especially 
conspicuous  at  the  higher  elevations  of  mountains,  where  the 
temperature  changes  are  very  great  and  abrupt ;  and  also  in  the 
clear  atmosphere  of  deserts,  where  owing  to  the  extent  and 
suddenness  of  temperature-  changes  between  day  and  night, 
caused  by  the  free  radiation  of  heat  into  the  clear  sky.  even 
homogeneous  pebbles  are  known  to  be  almost  explosively  dis- 
rupted in  the  mornings  and  evenings  of  clear  days. 

T 


2  SOILS. 

Such  effects  may  often  be  strikingly  observed  on  small  sur- 
faces of  compound  crystalline  rocks,  such  as  granite,  exposed 
on  glaciers,  where  the  daily  changes  of  temperature  are  often 
extreme,  viz.,  from  below  the  freezing  point  to  as  much  as 
130  degrees  Fahrt  (54.4  degrees  C).  In  such  cases  one  may 
sometimes  scoop  off  the  disintegrated  rock  by  the  handful, 
while  yet  the  mineral  surfaces  are  almost  perfectly  fresh. 

On  a  larger  scale,  the  disruption  and  scaling  off  of  huge 
slabs  of  granite,  and  rocks  of  similar  structure,  may  be  observed 
in  southern  California  on  the  southwestern  side  of  rock  ex- 
posures, where  slabs  from  a  few  inches  to  ten  and  more  feet 
in  length  and  eight  or  ten  inches  thick,  have  slid  off,  perhaps 
still  leaning'  against  the  parent  rock,  which  has  been  rounded 
off  by  a  succession  of  such  events  into  the  domelike  form  so 
characteristic  of  granite  mountains.  Merrill  J  reports  similar 
exfoliations  to  occur  especially  on  the  peninsula  of  California, 
on  Stone  Mountain  in  Georgia,  and  elsewhere. 

A  striking  exemplification  of  the  effects  of  frequent  and 
rapid  changes  of  temperature  on  rocks,  and  of  humid  and  dry 
climates  as  well,  is  seen  in  the  case  of  the  great  monoliths  of 
Egypt,  one  of  which  now  stands  in  the  Central  Park,  Xew 
York.  In  the  quarries  of  Syene  in  Upper  Egypt,  where  most 
of  these  monoliths  were  obtained,  the  rough  blocks  that  were  in 
progress  of  quarrying  when  the  work  was  abandoned,  quite 
two  thousand  years  ago,  still  show  an  almost  perfectly  fresh 
surface;  and  the  same  is  true  of  the  finished  obelisks  in  Lower 
Egypt,  where  both  the  changes  of  temperature  and  the  rain- 
fall are  somewhat  greater.  It  is  a  matter  of  public  note  that 
one  of  "  Cleopatra's  Needles  "  which  was  set  up  in  Central 
Park  nearly  thirty  years  ago,  but  originally  erected  at  Helio- 
polis  on  the  Nile,  is  in  great  danger  of  destruction  from  the 
influence  of  a  totally  different  climate,  in  which  both  the 
temperature  changes  and  the  rainfall  are  much  more  frequent 
and  severe  than  in  Egypt.  The  large  crystals  of  feldspar  and 
quartz  which  compose  the  (syenite)  rock  material  have  had 
fine  fissures  formed  between  them  by  often-repeated  expansion 
and  contraction ;  which  when  filled  with  water  and  subsequently 

1  See  Rocks,  Rock-weathering,  and  Soils,  page  246 ;  also  paper  on  Domes  and 
Dome  Structure,  by  G.  K.  Gilbert,  in  Bulletins  of  the  Geol.  Society  Am.,  Vol.  15,. 
pp.  29-36. 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.         3 

changed -to  ice,  the  latter' s  expansion  in  freezing  (see  below) 
has  still  farther  enlarged  them  and  caused  a  scaling-off,  which 
threatens  to  obliterate  the  hieroglyphic  inscriptions.  Thus 
temperature-changes  and  a  rain  followed  by  freezing  may 
in  a  few  days  produce  a  greater  effect  than  a  thousand  years 
of  Egyptian  climate. 

Cleavage  of  rocks. — Many  kinds  of  rocks  have  definite  direc- 
tions of  ready  cleavage.  The  most  common  and  obvious  cases 
of  this  kind  are  schists,  slates  and  shales,  cleaving  readily  into 
plates  or  irregular  flat  or  lens-shaped  fragments.  Such  struc- 
ture greatly  favors  disintegration,  especially  when  the  layers 
are  on  edge  at  steep  angles.  But  there  are  other  apparently 
structureless,  massive  rocks,  particularly  basalts  and  other 
eruptive  rocks  related  to  them,  as  well  as  many  sandstones  and 
claystones,  that  have  a  strong  tendency  to  cleave  into  more  or 
less  definite  forms  when  struck ;  such  as  columns  or  prisms, 
square,  six-sided  or  diamond-shaped  blocks,  etc.  Similar  forms 
are  naturally  produced  in  them  under  the  influence  of  changes 
of  temperature ;  by  the  formation  of  minute  cracks  at  first,  then 
enlargement  of  these  by  the  several  agencies  already  mentioned. 

Effects  of  freezing  water. — The  irresistible  force  exerted 
by  the  expansion  of  water  in  freezing,  amounting  to  about  9 
per  cent  of  its  bulk,  is  a  powerful  factor  in  widening  and  deep- 
ening fissures  and  cracks  of  rocks;  not  uncommonly,  whole 
masses  of  rock  are  rent  into  fragments  by  this  agency,  which 
is  one  of  the  most  common  causes  of  "  rock  falls  "  on  the 
brink  of  precipices.  By  the  freezing  process  cracks  and  crevices 
are  enlarged,  and  the  surfaces  exposed  to  weathering  are  still 
farther  increased ;  and  the  rock  fragments  or  soil  particles  are 
loosened  and  rendered  more  liable  to  be  removed  from  the 
original  site,  whether  by  gravity,  wind  or  water. 

Glaciers. — Tee  in  the  form  of  the  glaciers  that  descend  from 
mountain  chains  (see  figure  i).  and  of  the  moving  ice  sheets 
that  have  covered  large  portions  of  North  America  and  Europe 
in  past  ages  and  now  cover  Greenland  and  the  South  Polar  con- 
tinent, exerts  a  most  potent  action  in  abrading  and  grinding 
even  the  hardest  rocks:  not  so  much  by  the  direct  friction  of 
the  moving  ice  itself,  as  by  the  cutting,  scoring,  grinding  and 
crushing  action  which  the  stones  imbedded  in  the  ice,  or  carried 


4  SOILS. 

and  shoved  by  it,  exert  upon  the  rocky  channels  in  which  the 
ice  stream  moves,  as  well  as  upon  each  other.  The  product 
of  this  grinding  process  is  largely  very  fine  (hence  "  glacier 
flour"),  so  that  it  remains  suspended  in  the  water  of  the 
glacier-streams  until  their  velocity  is  permanently  checked 
when  reaching  a  plain  or  lake.  This  suspended  stone-flour 
imparts  to  the  glacier  streams  their  distinctive  character  of 
"  white  rivers,"  as  contradistinguished  from  the  clear,  dark 
"  green  rivers  "  that  have  their  origin  outside  of  glaciated 


FIG.  i. — Zermatt  Glacier  (Agassiz). 

areas.  This  difference  can  be  readily  observed  in  traveling 
along  any  of  the  glacier-bearing  mountain  chains  of  the  world, 
and  is  frequently  expressed  in  the  names, of  the- streams. 

The  physical  analysis  of  mud  from  the  foot  of  Muir  glacier,1 
Alaska,  at  its  sea  front,  made  by  Professor  Loughridge,  shows 
the  prevalent  fineness  of  the  materials  brought  down  by  the 
glacier  waters. 

1  Collected  by  Dr.  W.  E.  Ritter  of  the  University  of  California. 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.          5 

PHYSICAL  COMPOSITION'   OF   GLACIER   MUD. 


MATERIAL. 

DIAMETF.R. 

PER  CENT. 

Clay  

> 

I6.57  I 

Fine  silt  

.0023  —  .016  mm. 

S3  74    7°'31 

P  ine  silt  

.016    to  .025  mm. 

4.^8 

Medium  silt  

.025    to  .036  mm. 

HO 

7.06 

Coarse  silt  

.036    to  .047  mm. 

C..QI 

Coarse  silt  

.047    to  .072  mm.1 

3-J' 
-3.76 

Fine  sand       

.072    to  .1  2     mm. 

1.  14 

Medium  sand.  .    

.12      to  .16     mm. 

I   r6 

Total  

94.12 

It  will  be  noted  that  over  70  per  cent  of  this  mud  consists 
of  extremely  fine,  wholly  impalpable  materials ;  but  little  of 
which  is  true  clay. 

The  fineness  of  the  glacier-flour  renders  it  peculiarly  suitable 
for  the  rapid  conversion  into  soil,  and  such  soils  are  usually 
excellent  and  remarkably  durable.  The  great  and  lasting 
fertility  of  the  soils  of  southern  Sweden  is  traced  directly  to 
this  mode  of  origin,  and  doubtless  the  great  American  ice 
sheet  of  glacier  times  is  similarly  concerned  in  the  high  quality 
of  the  soil  of  our  ''  north  central  "  states,  from  the  Ohio  to 
the  Great  Lakes  and  the  Missouri. 

The  accumulations  of  rocks  and  debris  of  all  sizes,  in  the 
*'  moraines  "  or  detrital  deposits  of  glaciers  and  ice-sheets  form 
another  class  of  glacier-made  lands  which  cover  extensive  and 
important  agricultural  areas  (drift  areas),  both  in  the  old  and 
new  worlds.  Such  lands  are  undulating  or  slightly  hilly,  and 
the  soil  usually  contains  imbedded  in  it  stones  of  a  great 
variety  of  kinds  and  sixes,  partly  angular,  partly  rounded  and 
polished  by  friction.  Of  course  the  frequent  and  violent 
changes  of  temperature  occurring  on  the  surface  of  a  glacier, 
aid  materially  in  reducing  the  rocks  carried  by  it  to  the  con- 
dition in  which  we  find  the  material  of  the  moraines;  which 
commonly  form  lateral  or  cross  ridges  in  valleys  formerly 
occupied  by  glaciers. 

Action  of  flowing  7<.'<;/<v. — The  action  of  flowing  water  is 
doubtless  at  this  time  the  most  potent  mechanical  agency  of 
soil  formation.  From  the  sculpturing  of  the  original  simple 
forms  in  which  geological  agencies  left  the  earth's  surface 


6  SOILS. 

into  the  complex  ones  of  modern  mountain  chains,  to  the 
formation  of  valleys,  plains,  and  basins  out  of  the  materials  so 
carried  away,  its  effects  are  prodigious.  The  torrents  and 
streams  in  carrying  silt,  sand,  gravel  and  bowlders,  according 
to  velocity  and  volume,  do  not  merely  displace  these  materials ; 
the  rock  fragments  of  all  sizes  not  only  score  and  abrade  the 
bed  of  the  rill  or  stream,  but  by  their  mutual  attrition  produce 
more  or  less  of  fine  powder  siirilar  to  that  formed  by  glacier 
action ;  usually  more  mixed  in  its  ingredients  than  the  former, 
because  derived  from  a  wider  range  of  drainage  surface.  In 


FIG.  2. — Erosion  of  Hawaiian  Hills,  near  Honolulu.     (Phot,  by  H.  C  Myers.) 

the  glacier  stream  itself,  it  is  easy  to  trace  the  gradual  transi- 
tion from  the  sharp  stone  fragments  lying  in  the  water  as  it 
issues  from  the  terminal  ice  cave  at  the  lower  end  of  the 
glacier,  to  the  rounded  shingle  found  a  few  miles  below. 
On  slopes  where  water  flows  only  during  rain  or  the  melting 
of  snow,  the  same  erosive  effects  may  be  seen  as  between  the 
heads  of  ravines  and  their  outlets.  (See  figure  2.)  It  is 
there  too  that  the  surprisingly  rapid  cutting-out  of  channels  by 
the  aid  of  water  charged  with  rock  fragments  or  gravel,  can 
readily  be  observed,  and  the  enormous  power  of  water 
erosion  convincingly  shown.  In  the  United  States  the  stu- 
pendous gorges  of  the  Columbia  and  Colorado  rivers,  the 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.  7 

former  cut  to  a  depth  of  over  2000  feet  into  hard  basalt  rock, 
the  latter  to  over  5,000  feet,  partly  into  softer  materials,  partly 
into  granite,  are  perhaps  the  most  striking  examples  of  this 
power;  the  manifestations  of  which  can,  however,  be  as  con- 
vincingly seen  in  thousands  of  minor  rivers  and  streams. 

All  the  materials  so  carried  off  from  the  higher  slopes  are 
finally  deposited  on  a  lower  level ;  whether  only  a  short  distance 
away  on  a  lower  slope  (colluvial  soils),  or  farther  away  in  the 
flood  plain  of  streams,  rivers,  or  lakes  (alluvial  soils).  Other 
things  being  equal,  the  finest  materials  are  of  course,  carried 
farthest,  and  often  into  the  sea ;  in  which,  however,  they  can- 
noj  long  remain  suspended,  but  are  quickly  thrown  down, 
forming  river  bars,  flood  plains,  and  deltas.  The  fineness  of 
the  material  of  delta  soils,  like  that  of  those  made  from  glacier 
flour,  insures  them  the  same  advantage,  viz.  great  fertility  and 
durability. 

It  is  calculated  that  the  Mississippi  River  carries  into  the 
Gulf  of  Mexico  annually  some  7469  millions  of  cubic  feet  of 
earthy  deposits,  which  would  fill  one  square  mile  of  surface 
to  the  height  of  268  feet,  or  would  cover  that  number  of  square 
miles  to  the  depth  of  one  foot. 


FIG.  3. — Cliffs  and  caves  on  sea  beach  at  l.a  Jolla,  Calif,  slum  ing  effects  of  \Vave  action. 

Wave-Action. — The  powerful  effects  of  the  beating  of  wave? 
upon  abrupt  shores  of  seas  or  lakes  are  in  evidence  all  over 
the  world,  and  these  effects  are  so  characteristic  that  they  can  be 
recognized  even  where  no  sea  or  lake  exists  at  present.  Gravel 
and  sand  are  carried  in  the  surf  and  serve  as  grinding  ma- 
terials, wearing  even  the  hardest  rocks  into  grooves,  rills,  chan- 


8  SOILS. 

nels  and  caves,  defining  sharply  the  varying  degrees  of  hard- 
ness or  tough  resistance  in  different  parts  of  rocky  cliffs; 
frequently  undermining  them  and  causing  extensive  rock-falls. 
The  latter  then  serve  for  a  time  to  break  the  violence  of  the 
waves'  onset,  and  may  even  cause  permanent  shore  deposits  to 
be  formed  under  their  lee. 

Such  deposits  are  very  generally  formed  on  gently  sloping 
beaches,  and  as  the  water  gradually  recedes,  sometimes  by 
elevation  of  the  ground,  beach  lines  or  beach-terraces  are  left, 
which  indicate  the  successive  levels  of  the  lake  or  sea.  Such  old 
beach  lines  or  terraces  and  level-surfaced  "  buttes  "  in  the  Great 
Basin  country,  and  "  bench  lands  "  elsewhere,  show  in  their 
structure  the  characteristic  lines  of  wave-deposition. 

Effects  of  Winds. — The  action  of  winds  in  transporting  soil 
particles  (dust  and  sand)  is  familiar;  and  the  accumulations 
that  may  be  formed  under  the  influence  of  regular,  continuous 
winds  are  sufficiently  obvious  on  lee  shores  having  sandy 
beaches,  inland  of  which  the  formation  of  sand  dunes  at  times 
assumes  a  threatening  magnitude.  Where  winds  are  irregular, 
frequently  reversing  their  direction,  of  course  the  local  effects 
will  be  less  obvious,  and  the  transportation  of  material  actually 
occurring  will  often  not  be  noticed.  Yet  there  can  be  no  doubt 
of  the  importance  of  wind  action  in  soil  formation,  and  there 
are  cases  in  which  no  other  agency  can  explain  the  facts  ob- 
served over  widely  extended  areas.  This  is  especially  true  with 
regard  to  the  soil  masses  of  the  high  plains  or  plateaus  of  the 
dry  continental  interiors,  where  not  only  the  regularity  of  the 
prevailing  winds,  but  also  the  structure  (or  absence  of  struc- 
ture) and  pulverulent  character  of  the  soil  itself,  renders  this 
the  only  rational  mode  of  accounting  for  its  presence  where  we 
find  it. 

The  effects  that  may  be  exerted  by  regular  winds  are  well  illustrated 
in  the  plains  and  deserts  of  Africa  as  well  as  those  of  central  Asia. 
Here  we  find  a  distinct  subdivision  of  the  desert  (rainless)  areas  into  the 
stony,  from  which  the  wind  has  swept  all  but  the  bedrock  and  gravel  and 
where  scarcely  any  natural  growth,  and  certainly  no  cultivation  is  pos- 
sible in  the  almost  total  absence  of  soil.  The  next  subdivision  is  the 
sandy  desert,  to  leeward  of  the  stony  area,  where  the  winds  are  less 
violent  and  regular,  and  where,  therefore,  the  sand  has  been  dropped 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.          9 

and  is  wafted  back  and  forth  by  "  sand  storms,"  the  surface  being  covered 
with  moving  sand  dunes.  Still  farther  to  leeward  we  find  the  region  in 
which  the  finer  portions  of  the  desert  surface  has  been  deposited  ;  here 
we  have  "dust  storms"  so  long  as  the  land  is  not  irrigated;  but  the 
application  of  water  renders  the  soil  abundantly  fruitful.  Such  is  the 
case  of  the  Oases  and  fertile  border-lands  of  the  Sahara  and  Libyan 
deserts. 

In  the  cultivated  portions  of  the  Mojave  and  Colorado 
deserts  in  California,  plowing  of  the  land  during  a  dry  time  is 
not  uncommonly  followed  by  a  bodily  removal  of  the  loosened 
soil  to  neighboring  fields,  sometimes  leaving  a  gravel  surface 
behind.  Such  "  blown-out  lands  "  exist  naturally  at  numerous 
points  in  the  Colorado  desert. 

Sven  Heclin  (Central  Asia  and  Tibet,  Vol.  II.)  shows  that 
from  the  effects  of  the  violent  storms  that  prevail  in  the  Gobi 
or  Takla  Makan  desert,  Lop-nor  lake,  the  sink  of  the  Tarim 
river,  has  in  the  course  of  time  shifted  its  bed  as  much  as 
«£fty  miles  in  consequence  of  the  excavation  of  the  southern 
part  of  the  desert  by  the  wind ;  while  the  sand  so  blown  out, 
together  with  the  dejx>sits  from  the  rivers,  now  tends  to  fill 
up  the  present  (southern)  lake,  which  is  gradually  returning 
northward  toward  its  original  site,  now  a  desert,  but  around 
which  formerly  a  dense  population  existed. 

The  great  plains  of  North  America,  the  pampas  of  South 
America,  the  plateaus  of  Mongolia  and  especially  the  fertile 
loess  region  of  northwestern  China,  are  also  cases  in  point. 
The  dense  dust  stonws  of  these  regions  are  familiar  and  un- 
pleasant phenomena,  which  are  often  observed  even  by  vessels 
at  sea  off  the  east  coast  of  South  America,  where  the  dust-laden 
"pamperos  "  at  times  compel  them  to  proceed  with  the  same 
precautions  as  in  a  fog;  and  the  same  is  true  of  the  northeast 
winds  blowing  off  the  Sahara  desert  011  the  west  coast  of 
A  frica. 

The  effects  of  windstorms  carrying  sand  in  the  erosion  of 
rocks  are  very  obvious  and  striking  in  many  parts  of  the  world  ; 
nowhere  probably  as  much  so  as  on  the  great  plains  of  western 
North  America,  where  the  geological  composition  of  the  "  bad 
lands"  is  frequently  impressed  upon  the  rock  surfaces  very 
prominently.  The  strikingly  grotesque  forms  are  frequently 


10 


SOILS. 


brought  out  in  this  way,  especially  in  the  case  of  "  mush- 
room "  rocks,  where  a  hard  stratum  has  remained  as  a  covering 
while  softer  layers  underneath  have  been  worn  away.  The 
illustration  annexed  shows  such  a  case  on  the  plains  of  Wyom- 
ing as  figured  in  the  Report  of  the  U.  S.  Geological  Survey, 
on  the  Central  Great  Plains,  by  N.  H.  Darton.  Striking  ex- 
amples of  the  same  effects  are  seen  on  the  shores  of  Lake 
Michigan  in  the  Grand  Traverse  region,  where  the  rocky  cliffs 
are  visibly  worn  away  and  carved  under  the  influence  of  the 
regular  "  sand-blasts "  of  northwest  winds.  On  a  smaller 
scale  the  effects  of  these  sand-blasts  mav  be  noted  in  the  cob- 


O 


FIG.  4. — "Mushroom  rocks."  produced  by  Wind  action,  Wyoming.     (Darton.) 

ble-deserts,  where  we  frequently  find  the  cobbles  worn  away 
on  the  windward  side  in  a  very  characteristic  manner;  the  lee 
side  remaining  rounded  and  smooth,  while  the  structure  of  the 
rock  is  strongly  outlined  on  the  windward  side. 

CLASSIFICATION    OF    SOILS. 

The  physical  Constituents  of  soils  are  thus,  in  the  most  gen- 
eral terms,  first,  rock  pozvder  ("  sand  ")  more  or  less  changed 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.         n 

by  weathering;  second,  clay,  as  one  of  the  chief  results  of  the 
weathering /process  of  silicate  minerals;  and  thirdly,  humus,  the 
darK-colored  remnant  of  vegetable  decay.  According  to  the 
obvious  predominance  of  one  or  the  other  of  these  primary 
ingredients,  soils  are  popularly,  in  the  most  general  sense, 
classed  as  "heavy"  and  "light";  the  former  term  corre- 
sponding as  a  rule  to  those  in  which  clay  forms  a  prominent 
ingredient,  while  sandy  and  humous  or  "  mold  "  soils  usually 
fall  under  the  latter  designation,  because  of  their  easy  tillage. 
For  practical  purposes  these  subdivisions  are  both  convenient 
and  important,  and  they  form  the  ordinary  basis  of  land  class- 
ification. Beyond  these,  the  degree  of  fineness  of  the  rock  de- 
bris, and  their  physical  and  chemical  constitution,  determine 
distinctions  such  as  gravelly,  sandy,  silty,  loamy,  calcareous, 
siliceous,  magnesian,  ferruginous,  and  others  of  less  general 
application,  though  locally  often  of  considerable  importance. 

For  the  purposes  of  discussion  and  definition,  however,  an- 
other basis  of  classification  is  needed,  which  essentially  con- 
ns both  the  origin  and  the  adaptations  of  lands. 

UPLAND 
Plateau 


'Scab  ,  o,il       Sedentary  Soil 

Land 


FiG.  5. —  Diagram  illustrating  the  genetic  relation  of  different  soil  classes  to  each  other. 


I.  Sedentary  Soils. — When  soils  have  been  formed  without 
removal  from  the  site  of  the  original  rock,  by  simple  weather- 
ing, they  are  designated  as  sedentary,  or  residual  soils,  or 
"  soils  in  place."  In  the  case  of  these,  the  original  rock  under- 
lies the  soil  or  subsoil  at  a  greater  or  less  depth,  according  to 
the  intensity  and  duration  of  the  weathering  process,  and  is 
usually  more  or  less  softened  and  decomposed  at  the  surface 
where  it  meets  the  soil  layer.  The  latter  of  course  bears  some 
of  the  distinctive  characters  of  the  parent  rock,  and  its  composi- 
tion and  adaptations  may.  in  a  measure,  be  directly  inferred 
from  that  origin.  Such  soils  usually  contain,  especially  in  their 
lower  portions,  some  angular  fragments  of  the  parent  rock.  In 


i2  SOILS. 

some  cases  sedentary  soils  may  have  been  partially  derived 
from  rocks  that  have  been  removed  from  above  the  present 
country  rock  by  erosion,  and  in  that  case  fragments  of  such 
vanished  rock  may  also  be  present. 

Sedentary  soils  are  most  commonly  found  on  rock  plateaus 
and  on  slopes  or  plains  underlaid  by  rock  strata  of  but  slight 
inclination,  where  the  velocity  of  the  "  run-off  "  rainfall  is  not 
sufficient  to  dislodge  the  rock  debris.  Extended  areas  of  such 
soils  exist  in  the  granitic  areas  of  the  southern  Alleghanies,  in 
the  "  black  prairies  "  of  the  Cotton  States,  apd  on  the  "  basal- 
tic "  plateaus  of  the  Pacific  Northwest. 

2.  Cottuvial  Soils. — When  the  soil  mass  formed  by  weath- 
ering has  been  removed  from  the  original  site  to  such  a  degree 
as  to  cause  it,  to  intermingle  with  the  materials  of  other  rocks 
or  layers,  as  is  usually  the  case  on  hillsides,  and  in  undulating 
uplands  generally,  as  the  result  of  rolling  or  sliding  down, 
washing  of  rains,  sweeping  of  wind,  etc.,  the  mixed  soil,  which 
will  usually  be  found  to  contain  angular  fragments  of  various 
rocks,  and  is  destitute  of  any  definite  structure,  is  designat 
as  a  colluvial  *  one.     Colluvial  soil  masses  are  frequently  sur> 
ject  to  disturbance  from  landslides,  which  are  usually  the  result 
of  water  penetrating  underneath,  between  the  soil  mass  and 
the  underlying  rock,  or  sometimes  simply  of  complete  satur- 
ation of  the  former  with  water.    Aside  from  such  catastrophic 
action,  they  commonly  have  a  slow  downward  movement  in 
mass    (creep),  which  ordinarily  becomes  perceptible  only  in 
the  course  of  years ;  most  quickly  where  there  are  heavy  frosts 
in  winter,  which  act  both  by  direct  expansion,  and  by  the  state 
of  extreme  looseness  in  which  the  soil  mass  is  left  on  thawing. 
Colluvial  soils  form  a  large  portion  of  rolling  and  hilly  up- 
lands, and  are  of  very  varying  degrees  of  productiveness. 

3.  Alluvial  Soils. — When  soils  are  the  result  of  deposition 
by  streams,  the  material  having  been  gathered  along  the  course 

1  The  term  "  overplaced,"  used  for  such  soils  in  late  memoirs  of  the  U.  S.  Geo- 
logical Survey,  is  at  least  superfluous,  in  view  of  the  perfectly  understood  term 
already  in  general  use,  and  does  not  seem  to  commend  itself  for  adoption  by  any 
special  or  superior  fitness;  nor  does  the  suggestion  of  Shaler  (The  Origin  and 
Nature  of  Soils,  i2th  Rep.  U.  S.  Geol.  Survey)  to  include  the  colluvial  soils  within 
the  alluvial  class,  commend  itself  either  from  a  theoretical  or  practical  point  of 
of  view,  since  but  few  useful  generalizations  can  apply  to  both  classes. 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.          I3 

of  the  stream  from  various  sources  and  carried  to  a  distance 
before  being  deposited,  the  soil  is  designated  as  alluvial. 
These  are  the  soils  of  the  valleys,  flood-plains,  and  sea-  and 
lake-borders,  past  and  present.  Being  of  mixed  origin,  their 
general  character  may'  vary  from  one  extreme  to  the  other, 
both  as  regards  physical  and  chemical  composition.  Since, 
moreover,  they  represent  the  finer  portions  of  the  soils  of  the 
regions  drained  by  the  watercourses,  alluvial  soils  are  as  a  rule 
of  a  fine  texture ;  and  as  representing  the  most  advanced  de- 
composition products  of  the  parent  rocks,  they  are  usually 
preeminently  fertile.  This  is  proverbially  true  of  the  flood- 
plains  of  rivers,  and  still  more  of  their  deltas — the  bodies  of 
lands  formed  near  their  outlets  into  seas  or  lakes. 

Character  of  these  soil-classes. — Sedentary  soils  are  as  a 
matter  of  course,  other  things  being  equal,  dependent  entirely 
on  the  parent  rock  for  their  specific  character;  and  taking  into 
consideration  the  various  rocks  (usually  one  or  few)  from 
which  they  may  have  been  derived,  nearly  the  same  is  true  of 
Cfflluvial  soils,  except  that  a  portion  of  the  clay  and  finest  pul- 
verulent matters  may  in  their  case  be  carried  down  on  the 
lower  slopes  and  into  the  valleys  and  streams,  by  the  hillside 
rills. 

According  to  the  calculation  of  Merrill  (Rocks,  Rock-weathering,  and 
Soils,  p.  1 88)  granite  when  transformed  into  soil  without  loss  would 
increase  in  weight  by  88  fj,  ;  more  than  doubling  its  bulk.  More 
usually,  the  leaching  process  diminishes  their  volume  as  compared  with 
the  parent  rock. 

Alluvial  soils  are  also  of  course  to  a  certain  extent  de- 
pendent upon  the  character  of  the  rocks  and  surface  deposits 
occurring  within  the  drainage  area  of  the  depositing  stream. 
As  a  rule  their  composition  is  much  more  generalized;  but  their 
character  as  to  the  relative  proportions  of  sand  and  clay  is 
essentially  dependent  upon  the  velocity  of  the  water  current. 
Thus  in  the  upper  portions  of  valleys,  where  the  slope  is 
relatively  steep  and  the  velocity  therefore  high,  a  largo  pro- 
portion of  cobbles  and  gravel  is  often  present  in  the  deposits, 
sometimes  to  the  extent  of  rendering  cultivation  impracti- 
cable, or  at  least  unprofitable.  As  the  slope  and  velocity  do- 


I4  SOILS. 

crease,  first  coarse  and  then  fine  sand  will  be  the  prominent 
component  of  the  deposited  soil ;  while  still  lower  down,  in 
the  region  of  slack  water,  the  finest  sand  or  silt,  together 
with  clay,  will  predominate.^  v?\€cordi»g-ra  Hopkins,1  flowing 
water  will,  at  a  velocity  of  three  inches  per  second,  carry  in 
suspension  only  fine  clay  (and  silt)  ;  at  eight  inches  it  will 
carry  sand  as  large  as  linseed.  At  one  and  one-third  inches, 
it  will  move  pebbles  one  inch  in  diameter;  and  at  a  velocity  of 
two  inches  per  second,  pebbles  of  egg  size  are  moved  along  the 
stream  bed.  Since  the  velocity  of  streams  subject  to  freshets 
will  vary  greatly  from  time  to  time,  deposits  of  very  different 
grain  will  in  such  cases  be  found  alternating  with  one  another 
in  the  soil  stratum  of  the  flood  plain.  In  fact,  this  alternation 
and  the  more  or  less  stratified  structure  resulting  therefrom, 
is  the  distinguishing  mark  of  alluvial  soils  as  such.  It  is  true 
that  this  peculiarity  is  also  sometimes  found  in  the  case  of 
lands  now  lying  far  above  the  flood-plains  of  present  rivers; 
but  this  is  due  to  the  elevation  of  the  land  or  the  depression 
of  the  river  channels  at  a  former  period,  prior  to  which  such 
lands  (commonly  known  as  river  terraces,  benches  or  second 
bottoms)  were  formed.  The  same  is  true  of  lake  terraces 
("  mesas  "),  which  cover  enormous  areas  in  some  parts  of  the 
world,  more  particularly  in  western  North  America.  It  must 
nevertheless  be  remembered  that  such  alluvial  terrace  or  bench 
soils  differ  in  some  respects  from  the  modern  alluvials,  on 
account  of  their  long  exposure  to  atmospheric  action  alone; 
one  result  of  which  is  that  they  are  usually  much  poorer  in 
humus,  and  therefore  of  lighter  tints,  than  the  more  modern 
soils  of  alluvial  origin.  Other  differences  will  be  adverted 
to  hereafter. 

As  a  matter  of  course  the  above  distinctions,  especially 
between  colluvial  and  alluvial  soils,  cannot  be  rigorously 
maintained  in  all  cases.  There  are  transitions  from  one 
class  to  the  other,  so  that  it  is  sometimes  optional  with  the 
observer  to  which  of  the  two  classes  a  particular  soil  may 
be  considered  as  belonging.  On  the  lower  slopes  of  the  hills 
bordering  alluvial  valleys  the  colluvial  slope-soil  may  often 
be  found  alternating  with  the  alluvial  deposits,  or  bodily 

1  Geikie,  "  Text-book  of  Geology,  jd  ed. 


THE  PHYSICAL  PROCESSES  OF  SOIL  FORMATION.          15 

washed  away  to  be  redeposited  as  alluvium  at  a  greater  or  less 
distance. 

One  characteristic  of  the  flood-plain  lands  of  all  the  larger 
rivers,  and  more  or  less  of  all  streams  subject  to  periodic 
overflows,  is  that  the  land  immediately  adjoining  the  banks 
is  both  higher  and  more  sandy  than  are  the  lands  farther  back 
from  the  stream.  The  cause  of  this  phenomenon  is  that  as 
lateral  overflow  diminishes  the  velocity  of  that  flow,  its  coarser 
portions  are  deposited  near  the  river  banks,  while  the  finer 
particles  are  carried  farther  away,  until  finally  only  the  finest 
— clay-substance — reach  the  lagoons  or  lakes  filled  with  the 
overflow  or  back-water,  and  are  there  in  the  course  of  time 
deposited  as  heavy  clay  "  swamp  "  soils.  The  same  occurs 
where  rivers  empty  into  lakes  or  the  sea ;  and  these  slack-water 
or  delta  lands  are,  as  a  rule,  the  most  productive  on  the  river's 
course.  The  continued  productiveness  of  alluvial  soils  is  more- 
over in  many  cases  assured  by  the  deposition,  during  overflows, 
of  fresh  soil-material  brought  down  from  the  head  waters  of 
the  streams.  The  Nile,  and  the  Colorado  river  of  the  West, 
illustrate  this  point. 

Lowering  of  the  land-surface  b\  soil  formation. — It  is 
evident  that  the  soil-forming  agencies  must  in  the  course  of 
time  materially  affect  both  the  surface  conformation  and  the 
absolute  level  of  the  land.  The  sharp  pinnacles  and  crests  of 
rock  are  abraded  into  the  rounded  forms  now  characterizing 
our  uplands  and  lower  ranges  of  hills  and  mountains;  and 
it  is  estimated  that,  c.  g.,  the  general  level  of  the  drainage  basin 
of  the  Mississippi  river  is  lowered  about  one  foot  in  7.000 
years,  the  material  being  carried  into  the  lowlands  and  the  sea. 


CHAPTER  II. 


THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION. 
Chemical  Disintegration,  or  Decomposition. 

IT  may  be  said  that  in  general,  the  physical  agencies  of  dis- 
integration are  most  intensely  active  in  the  dry  or  arid  regions 
of  the  globe,  while  chemical  processes  of  decomposition  are 
most  active  in  humid  climates. 

The  chemical  decomposition  of  rocks  is  primarily  due  to  the 
action  of  the  atmosphere;  the  average  composition  of  which 
may  be  stated  as  follows : 


VOLUME  PER  CENT. 

WEIGHT  PER  CENT. 

Nitrogen  

78.00 

7c.;c 

Oxygen     .  .  :  „  

2I.OO 

23.22 

Carbonic    dioxid  

O7-.O4 

.O45~.o6o 

Ammonia     

i  to  4  millionths 

\Vater   vapor  

Variable  •  48  to  83  grams  per 

cubic  meter,  when  satu- 
rated   between    O    and 
50°C. 

In  addition  to  the  above,  air  contains  minute  amounts  of  the 
very  indifferent  and  therefore  practically  negligible  elements, 
argon,  krypton,  neon,  xenon  and  helium,  the  aggregate  amount 
of  which  in  air  is  somewhat  less  than  one  per  cent,  of  which  the 
greater  part  is  argon.  So  far  as  known  these  elements  take 
no  part  whatever  in  vegetable  or  animal  life,  and  possess  no 
known  chemical  action  or  affinity. 

The  primary  active  agents  in  effecting  chemical  changes 
in  rocks  by  which  soils  are  formed,  are  water,  carbonic  acid,1 
and  oxygen ;  all  therefore  ingredients  of  the  atmosphere. 
Hence  the  chemical  changes  so  brought  about  are  in  the  most 
general  sense  comprehended  within  the  term  weathering,  as 

1  Owing  to  the  universal  presence  of  water  (H2O)  in  air  as  well  as  in  soils,  it  is 
usual  and  convenient  to  speak  of  carbonic  dioxid  (CO2)  gas  when  so  occurring  as 
carbonic  acid  (HaCOs),  of  which  it  produces  the  effects  (CO3+H2O=H2CO3). 

16 


THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION.         I7 

applied  to  rocks;  while  the  corresponding  but  more  complex 
action  within  the  soil  itself  is  usually  termed  fallowing. 

Effects  of  Water. — Since  but  few  substances,  particularly 
among  those  forming  rocks,  are  totally  insoluble  even  in  pure 
water,1  and  some  (such  as  gypsum)  may  be  considered  easily 
soluble  in  the  same,  the  rain  water  must  exert  solvent  action 
wherever  it  penetrates.    In  nature,  however,  strictly  pure  water  i 
does  not  occur,  it  being  difficult  to  obtain  it  even  artificially.  \ 
Among  the  "  impurities  "  almost  always  contained  in  natural 
water,  there  are  several  that  materially  increase  its  solvent 
power.     Foremost  among  these,  both  because  almost  univer- 
sally present  and  on  account  of  its  great  ultimate  efficacy,  is 

Carbonic  dio.vid,  in  contact  with  water  forming  carbonic 
acid,  the  acidulous  ingredient  of  all  effervescent  waters,  the 
gas  which  is  produced  in  nature  by  innumerable  processes, 
such  as  decay,  putrefaction,  fermentation,  the  slow  or  rapid 
combustion  of  vegetable  and  animal  substances,  such  as  wood, 
charcoal  and  all  other  fuels;  by  the  respiration  of  animals; 
in  the  burning  of  limestone,  etc.  It  is  therefore  of  necessity 
contained  in  air,  on  an  average  to  the  extent  of  about  1-3000  of 
its  bulk  in  the  general  atmosphere,  but  locally  in  considerably 
higher  proportions  because  of  proximity  to  sources  of  forma- 
tion, and  of  its  greater  density  as  compared  with  air  ( i  ]/2  as 
against  i).  It  may  thus  accumulate  in  inhabited  buildings,  in 
cellars,  wells,  mines,  caves ;  and  it  is  contained  in  considerable 
proportion  in  the  air  of  the  soil.  Moreover,  being  easily  soluble 
in  water  (to  the  extent  of  an  equal  volume  at  the  ordinary 
temperature  and  barometric  pressure)  it  is  contained  in  all 
natural  water,  whether  of  rains,  rivers,  springs  or  wells,  and 
largely  of  course  in  that  percolating  the  soil.  Such  waters 
may  therefore  be  considered  as  being  acid  solvents;  and  as 
such,  they  exercise  a  far  more  energetic  and  far-reaching  effect 
than  would  pure  water. 

Carbonated  water  a  universal  solvent. — While  limestones 
are  the  rocks  most  obviously  acted  upon  by  carbonated  water, 
few  if  any  resist  it  altogether.  Even  quartz  rocks  of  the  ordi- 
nary kinds  are  attacked  by  it ;  only  the  purest  white  crystalline 
quartzite  may  be  considered  as  sensibly  proof  against  it. 

1  See  Chapter  18. 


1 8  SOILS. 

Granite  and  the  rocks  related  to  it  are  rather  quickly  acted  upon, 
because  of  the  presence  of  the  feldspar  minerals  containing 
potash,  soda  and  lime  as  bases  1  together  with  alumina. 

The  results  of  this  action  are  highly  important;  one  being 
the  formation  of  clay,  so  essential  as  a  physical  ingredient  of 
soils;  the  other  the  setting-free  of  potash,  one  of  the  most 
essential  nutrients  of  plants.  Hornblende  and  the  related 
minerals  are  similarly  acted  upon  so  far  as  they  contain  the 
same  substances.  In  all  cases,  of  course,  the  silica  (silicic  acid) 
set  free  by  the  carbonic  acid  remains  partially  or  wholly  in  the 
resulting  soils,  as  such.  Lime  also  at  first  mostly  remains 
behind  in  the  form  of  the  carbonate ;  but  potash  and  especially 
soda  compounds,  being  mostly  readily  soluble  in  water,  are 
largely  carried  away  by  the  latter. 

The  effect  of  carbonated  water  upon  silicate  minerals  is 
greatly  increased  by  the  presence  of  ammonia  (ammonic  car- 
bonate), which  always  exists  in  atmospheric  water  to  a  greater 
or  less  extent.  This  effect  may  readily  be  noted  on  the  win- 
dows of  stables,  or  other  places  where  animal  offal  decays, 
by  the  dimming  of  the  glass  surfaces;  also  in  glass  bottles 
containing  solution  of  ammonic  carbonate. 

Action  of  Oxygen. — The  effects  of  atmospheric  oxygen  on 
rocks  are  of  course  confined  to  those  containing  substances 
capable  of  farther  oxidation.  Chief  among  these  are  ferrous 
(iron  monoxid)  and  ferroso- ferric  oxid  the  latter  imparting 
bottle-green,  bluish  and  black  tints  to  so  many  minerals  and 
rocks  that  these  colors  may  usually  be  taken  as  indicating  its 
presence.  By  taking  up  more  oxygen  the  ferrous  and  ferroso- 
ferric  oxids  are  converted  into  ferric  oxid  or  its  hydrate  (rust), 
the  tints  mentioned  passing  thereby  into  brick-red  or  rust  color, 
according  as  the  former  or  the  latter  (or  sometimes  their  in- 
termixtures) is  formed.  In  either  case  there  is  an  increase  in 
bulk;  and  this  when  taking  place  in  the  cracks  or  crevices  of 
minerals  or  rocks,  tends,  like  the  freezing  of  water,  to  widen 

1  The  increase  of  solvent  power  on  feldspar  when  carbonated  instead  of  distilled 
water  is  used,  was  well  exemplified  in  an  experiment  made  by  Ileadden  (Bull. 
65,  Color.  Exp't  Sta.,  p.  29),  who  allowed  pure  distilled  and  carbonated  water 
respectively  to  act  on  fresh  but  finely  pulverized  feldspar,  with  frequent  shaking, 
for  five  days.  The  distilled  water  disolved  .0081  gram,  the  carbonated  water, 
.0723  gram  of  solids,  or  nearly  nine  times  as  much  as  the  distilled  water.  Both 
residues  gave  strong  reactions  for  potash  with  platinic  chlorid. 


THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION.         jg 

the  cracks  and  thus  to  increase  the  surface  exposed  to  attack. 
Since  ferrous  compounds,  when  soluble  in  water,  are  injurious 
to  plant  growth,  this  oxidation  is  of  no  little  importance,  and 
in  soils  must  be  carefully  maintained  against  a  possible  reversal. 
It  is  hardly  necessary  to  insist  that  the  action  of  all  these 
chemical  agents  continues  in  the  soils  themselves,  and  that 
owing  to  the  fineness  of  the  material,  resulting  in  an  enor- 
mously increased  surface  exposed  to  attack,  such  action  ac- 
quires increased  intensity.  This  is  the  more  true  as  in  soils 
bearing  vegetation  there  are  always  superadded  the  effects 
of  the  humus-acids  resulting  from  the  decay  of  vegetable 
matter,  as  well  as  of  the  acid  secretions  of  the  living  plants. 

Action  of  Plants  and  their  Remnants  in  Soil  Formation. 

(a}  Mechanical  action. — The  direct  action  of  plants  in  forc- 
ing their  roots  into  the  crevices  of  rocks  and  minerals  and  thus 
both  widening  them  by  wedging,  and  by  exposing  new  sur- 
faces to  weathering,  has  already  been  alluded  to.  That  the 
mechanical  force  exerted  by  root  growth  is  very  great,  may 
readily  be  judged  from  their  effects  in  forcing  apart,  even  to 
rupture,  the  walls  of  rock  crevices ;  but  actual  measurement  has 
shown  the  force  with  which  the  root,  e.  g.,  of  the  garden  pea 
penetrates,  to  be  equal  to  from  seven  to  ten  atmospheres,  say 
from  200  to  over  300  pounds  per  square  inch.  Such  a  force, 
exerted  under  the  protection  of  the  corky  layer  protecting  the 
root  tips,  often  produces  surprising  effects. 

(b)  Chemical  action. — Vegetation  takes  a  most  important 
part,  from  a  chemical  point  of  view,  both  in  the  first  formation 
of  soils  and  in  their  subsequent  relations  to  vegetable  life.  The 
lower  forms  of  vegetation  are  usually  the  first  to  take  posses- 
sion of  rock  surfaces;  foremost  among  these  are  the  lichens. 
In  humid  climates  we  find  these  crust-like  plants  incrusting 
more  or  less  all  exposed  rock  surfaces,  sometimes  with  a  solid 
mantle  that  can  be  peeled  off  in  wet  weather,  showing  the 
corroded  rock-surface,  and  the  beginnings  of  soil  clustering 
amid  the  root-fibrils  beneath.  A  microscopic  examination  of 
the  substance  of  these  lichens  often  shows  as  a  prominent  in- 
gredient, crystals  of  oxalate  of  lime,  the  lime  having  of  course 
been  derived  from  the  rock,  while  the  oxalic  acid  has  been 


20  SOILS. 

formed  by  the  plant  and  used  in  the  corrosion  of  the  rock 
minerals.  When  it  is  remembered  that  this  acid  is  comparable 
in  strength  to  hydrochloric  and  nitric  acids,  the  energy  of  the 
attack  of  the  lichens  is  explained.  Its  progress  can  often  be 
traced,  even  beyond  the  visible  root  fibers,  by  a  change  in  the 
color  of  the  rock ;  c.  g.,  from  rust-color  to  brick  red. 

When  by  the  action  of  the  lichens  a  certain  depth  of  loosened 
rock  or  half- formed  soil  has  been  produced,  the  next  step  is 
usually  the  advent  of  various  mosses,  which  gradually  shade 
out  the  crust-like  lichens,  while  the  erect  kinds  persist  for  some 
time.  Eventually  the  mosses,  after  having  increased  still 
farther  the  soil  layer  on  the  rock  surface,  are  themselves  par- 
tially or  wholly  displaced  by  the  hardier  species  of  ferns ;  and 
with  these  the  higher  flowering  plants,  such  as  the  stonecrops 
and  saxifrages  (the  latter  deriving  their  name  from  their 
"rock-breaking"  effect),  the  heather,  and  many  other  or 
shallow-rooted  plants,  gradually  take  possession.  The  roots 
of  all  plants  secrete  carbonic  acid;  and  many  of  them,  much 
stronger  vegetable  acids,  such  as  oxalic  and  citric.  In  the 
crevices  of  rocks  we  commonly  find  the  roots  forming  a  dense 
network  over  the  surfaces,  the  marks  of  which  show  plainly  the 
solvent  effect  produced  on  the  rock  by  the  root  secretions. 
This  is  most  readily  observable  on  a  polished  marble  surface, 
or  on  feldspathic  rocks.  Of  course  the  progress  of  soil-forma- 
tion is  very  much  more  rapid  when,  as  in  the  case  of  powdered 
lava  (volcanic  ash)  and  rock  debris  resulting  from  the  effects 
of  frost  etc.,  the  surface  is  very  much  increased.  In  tropical 
climates,  where  both  vegetative  and  chemical  action  is  most 
intense,  it  takes  some  of  the  higher  plants  only  a  few  years 
after  a  volcanic  eruption  to  take  possession  of  portions  of  the 
"  ash  "  surfaces ;  thus  helping  to  form  a  soil  on  which  after  a 
few  more  years  agricultural  plants  such  as  the  vine  and  olive 
yield  paying  returns. 

To  this  direct  action  of  the  higher  plants  is  always  added, 
to  a  greater  or  less  extent,  that  of  innumerable  bacteria,  as 
well  as  molds;  whose  vegetative  and  secretory  action  mater- 
ially assists  that  of  the  roots,  and  the  weathering  process  in 
general. 

Humification. — While  the  mechanical  action  of  the  roots  and 
the  chemical  effect  of  the  acids  of  their  root  secretions  are  very 


THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION,         2I 

efficient  in  promoting  the  transformation  of  mere  rock  powder 
into  soil  material  proper,  the  efficacy  does  not  end  with  the 
life  of  the  plant.  In  the  natural  process  of  decay  to  which  the 
roots  are  subject  after  death,  and  which  also  affects  the 
leaves,  twigs  and  trunks  falling  on  the  surface,  the  vegetable 
matter  suffers  a  transformation  which  must  be  considered  more 
in  detail  hereafter,  and  results  in  the  formation  of  the  com- 
plex mixture  of  dark-tinted  substances  known  as  vegetable 
mold  or  humus;  the  remnant  of  vegetation  that  imparts  to 
surface  soils  their  distinctive  dark  tint.  Its  functions  in  soils 
are  both  numerous,  and  important  to  vegetable  growth ;  as  re- 
gards soil  formation,  it  assists  disintegration  of  the  rock  min- 
erals both  by  the  formation  of  certain  fixed,  soluble  acids  ca- 
pable of  acting  on  them  with  considerable  energy,  and  by  the 
slow  but  continuous  evolution  of  carbonic  acid  under  the  in- 
fluence of  atmospheric  oxygen,  which  has  been  alluded  to 
above. 

Causes  influencing  chemical  action  and  decomposition. — The 
chemical  processes  causing  rock  decomposition  are  of  course 
continued  in  the  soil,  and  there  also  are  materially  influenced 
by  climatic  and  seasonal  condition?,  which  bring  about  great 
differences  in  the  kind  and  intensity  of  chemical  action. 

Within  the  ordinary  limits  of  solar  temperatures  it  may  be 
said  that,  other  things  being  equal,  the  higher  the  temperature 
the  more  intense  will  be  chemical  action  in  soil  formation. 
Since,  however,  water  is  a  potent  factor  in  the  majority  of 
these  processes,  the  presence  or  absence  of  moisture  at  the  same 
time  with  heat  will  cause  material  differences  in  the  kind  and 
intensity  of  chemical  action.  In  view  of  the  importance 
of  carlxjnic  acid  as  a  chemical  agent,  the  presence  or  absence 
of  vegetable  matter  or  humus,  from  which  by  oxidation  or 
decay  carbonic  and  humus-acids  are  formed,  will  likewise  be 
of  material  influence. 

The  presumption  that  climatic  and  seasonal  conditions  must 
greatly  influence  both  the  kind  and  rapidity  of  the  soil-form- 
ing processes,  is  fully  Ixjrne  out  by  observation  and  practice. 
Especially  is  the  amount  and  distribution  of  rainfall  of  great 
importance  in  this  respect,  and  should  therefore  be  first  con- 
sidered. 


22 


SOILS. 


INFLUENCE  OF  RAINFALL  ON   SOIL  FORMATION;  LEACHING  OF 

THE  LAND. 

In  the  general  consideration  of  the  soil-forming  processes, 
it  has  been  stated  that  soils  formed  by  the  disintegration  of 
rocks  "  in  place,"  i.  e.,  without  removal  from  the  original 
locality,  are  also  designated  as  "  residual  " ;  meaning  thereby 
that  only  a  portion  of  the  original  rock  remains  to  form  the 
soil  mass,  while  another  portion  has  been  removed.  To  a  slight 
extent  this  removal  occurs  by  the  partial  washing-away  of  the 
finest  clay  and  silt  particles;  but  the  most  important  action 
from  the  agricultural  point  of  view  is  the  removal  by  leaching 
with  the  carbonated  water  of  the  atmosphere  and  soil,  of  cer- 
tain easily-soluble  compounds  formed  in  the  process  of  chemical 
decomposition  of  rocks  and  resultant  soils.  The  nature  of  these 
compounds  is  exemplified  in  the  subjoined  table  giving  the 
composition  of  some  waters  flowing  from  drains  in  unmanured 
fields,  laid  at  depths  of  from  two  to  three  feet ;  and  for  compari- 
son with  these,  the  composition  of  the  water  of  some  of  the 
world's  large  rivers,  showing  what  these  largest  drains  carry 
into  the  ocean. 

The  analyses  have  in  all  cases,  where  necessary,  been  re- 
calculated to  parts  per  million,  and  to  oxids,  from  the  published 
data. 

The  letter  "  c  "  indicates  that  the  preceding  figure  has  in  the 
absence  of  a  direct  determination  been  stoichiometrically  cal- 
culated from  the  data  given,  in  order  to  complete  the  com- 
parison. 

COMPOSITION    OF     DRAINAGE     WATERS     FROM    UNMANURED   GROUND. 
PARTS     PER     MILLION. 


ROTHAM- 
STBD. 
(VOHLKBR.) 

PROSKAU. 
(KROCKER.) 

MOCKKRN. 

(O.  WOLFF.) 

FARNHAM. 
(WAY.) 

MUNICH. 

(Z6LLER.) 

Rye 
Field. 

Mead- 
ow. 

Wheat 
Field. 

Hop 
Field. 

Lysemeter 
Drainage. 

Aver- 
age. 

Potash,  K,O  

'•7 
6.0 
98.1 

5-' 
5-7 

5-4 

11.7 

'24  3 
6-4 
44 

'5  ' 
'33-0 
33  3 

6.6 

2.0 

•3-7 
nS.i 
22.4 
6.6 

-•  =, 
23  3 

122.6 
14-9 

j-S.o 
7.0 

34 

8.2 

22.5 

6-7 
6.0 
4  ° 

Trace  . 
'43 
69-3 
9-7 

j  5-9 
'•35 

Trace 

45  7 
185.0 

r 

}  7-' 

12.  I 

6-5 
7-i 
145.8 
20.5 

2-4 
5-6 

57-6 
8.9 
6.3 

3-2 

107^6 
•6.3 

Soda    Na.O  .... 

Lime,  Cat)  

Iron  Oxid,  Fe,O,  

Silica    SiO,  

lo.q 

481 
•6j 

14-7 
10  7 

'54 
44  4 
9.1 
66.30 
II.  I 
5.  10 

7.0 
75.8 
Trace 
122.7 
4-8 

6.0 
82.6 
Trace. 
67.3 
42 

10.4 

11.3 

Carbonic  Acid,  CO,... 
Phos"  Acid,  PjO6  
Sulfuric  Acid,  SO,.... 
Chlorin  CI  . 

Trace. 
14.0 

19.0 
Trace. 

Trace. 

23-5 

IO.O 

'•7 
'358 

37-4 

2.2 

'7-5 
57-5 

Trace. 

27.1 
9-5 

o-5 
60.8 

'7-7 

Nitrogenas,  N.OS  

Nitro^enas,  NHj  

.11 

•'3 

•25 

.01 

Total  Mineral  Matter.. 
I^ss  O  :  CI  

iiS-9 
a.  35 

295  5 
24 

4°o  3 
1.1 

3Z*-9 

198.3 
3  ' 

191.1 

248.8    |62j.5 

22               8.1 

267.6 

128.7 

Corrected  Total  

"3-3 

22.9 

2Q3.I 
19  1 

399-3 
25.0 

322.0 
16.0 

195.2 
26.0 

191.1 
26.0 

246.6 
IOO.O 

615.3 
105.7 

254-9 
20.5 

126.6 

12.6 

285.7 

Organic  Matter  

Total  Solids.  .  . 

21C.2 

•l.-i 

1-4   - 

n8.o 

221.2 

217.  I 

^6.6 

7CI.6 

THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION. 


H 
o 

W) 

o_ 

Corrected  Totals  
Organic  Matter  

n  o 

?2 

1 

Sulfuric  Acid,  SO3.... 
Chlorin  Cl  

Ammonia,  NH3  

-:  : 
J.i 

J 

1 
^ 

w 
< 

||| 

-.  «     u>  ! 

J       &>          3 

3    n      5 
1  1     -     J 
»    5'     Q 

pi 

•o     ?S 

^1 

<o 

•o 

O 

00 

w 

^4           O 

ooH 

><; 

w"c 

•5  -3  '  Q 

O                     jy 

8 

8 

O    O 

o       o 

8   ?  §= 

O         O 

*"2 

»  3 

P 
OO  ^  &) 

w 

•Vj        M 

<-     w 

en 

<"    ^ 

«  - 

ll? 

3  g-3 

5'  P.  a-' 

i 

- 

S            M 

J 
< 

5  2   5       <? 

en         O 

»» 

jq   n   si 

H 
8,0' 

J*  8  5" 

w 

« 

« 

^ 

1 
1 

H^  w   :  : 

^ 

c/; 

r  ^r 
i-'S.r1 

0  =  5! 
V;  rr  S 

0   -,T« 

lil 

* 

" 

vyi    O 

O 

< 
( 

>t   ?  : 

"o      'o 

-s-s 

n  D.  2 
c*  n  3 

••sis 

" 

s 

^K 

K> 

Ln        CO        t** 

-         en 

w  - 

22 
o  •;"• 

s  s 

^!| 

2 

* 

O     N 

§           * 

1 
t. 

*    W      O            H 

co       o 

3     8 

-  o 

0    0 

=  1 

gn     ri 
f-     ™ 

s 

13 

o  <*» 

O           & 

So       o 

O 

O 

1 

J     2 

w  X 

0-3 

H.05 
"^  o 

£  *  £.-£ 

f*  en  '*•  ^~l 
O          »* 

w"~   ^    ^ 

sr?  3 

s* 

M 

•S     8 

0       ^ 

1  i' 

0    3 

"  o 

9  ,0    '      - 

O          OO 

^     :  : 

Pw  ?"  oo 

5' 

•<     " 
S    n 
r1    P 

0 

C/l 

Z  < 

O1 

j; 

u 

Oa 

-    * 

„ 

S" 

0 

r 

"*  ^  ^ 

& 

s 

c?^ 

*3      * 

Pi 

ss.  t  -a: 

cV  *o       o 

en    CO 
0    0 

S 

b 

C 

£.|<3  «  J1 

^  ~   wj 

S.      c1  '  ' 

o 

o 

00  w 

b  t^ 

8     8 

0       ;              ; 

«           CO 
0          IT 

•*•    CO 
0   0 

v$  d. 

r 
o|~| 
cn»^ 

Is 

00 

o  « 

o  r  r 

^  <a     :    '. 

o      >. 

00  O 

30  ^"  ~ 

X       < 

o  ^- 

•<    S.  3 
•      Sc 

8*? 

o  o 

ti 

O      e-        t-J 

l?\\ 

0        ^ 

0    O 

5,-- 

r 
H. 
3 

1 

9 

?! 

:     "o       S     o 

Jj 

CO      O 
-       CO         00 

o     o       o 

o      *o 

o  b 

?  ^^ 

S?  o"  ^ 

o*(^i  o  c 

1—  ^   «-»  1 

CT> 

t> 

11 

i! 

b    -^j       be 

^4       O          O       C 

1 

lOt* 

- 

Si.      -    bo  i. 
C       O    0    C 

'-J             M         K 

0          0       C 

o  o 

=-X£.> 

^  O    ft)  ^ 

24  SOILS. 

It  will  be  noted  that  in  all  the  drain  waters,  lime  is  the  in- 
gredient most  abundantly  leached  out,  and  as  reference  to  the 
acids  shows,  mainly  in  the  form  of  carbonate,  also  in  that  of 
sulfate.  Magnesia  is  next  in  amount  among  the  bases;  next 
in  amount  is  soda,  largely  in  the  form  of  sodium  chlorid  or 
common  salt.  Potash  is  present  only  in  small  but  rather  uni- 
form amounts.  Of  the  acids  the  carbonic  is  the  most  abundant, 
sulfuric  next;  chlorin  and  silicic  acid  come  next,  in  about 
equal  amounts.  Nitric  acid  passes  off  in  small,  but  still  rela- 
tively considerable  amounts. 

Comparison  of  the  drain  waters  with  the  river  waters,  while 
showing  a  general  qualitative  agreement,  also  shows  a  marked 
diminution  of  total  solids  (from  285.7  to  188.7;  hence  "  soft 
river  water"),  and  especially  of  lime  (from  107.6  to  43.2), 
together  with  the  carbonic  acid  with  which  it  is  mostly  com- 
bined ;  indicating  a  deposition  of  lime  carbonate  in  the  river 
deposits  or  alluvial  lands.  There  is,  on  the  other  hand,  little 
if  any  general  difference  in  the  magnesia  content  of  the  two 
classes  of  waters ;  nearly  the  same  is  true  of  soda,  so  that  these 
two  bases  really  show  a  considerable  relative  increase  when 
the  diminished  total  is  considered.  Potash  remains  about  the 
same  all  through,  viz.  two  parts  or  a  little  more ;  phosphoric 
acid  shows  a  fraction  of  one  millionth  ;  nitric  acid  varies  greatly 
but  is  usually  higher  in  the  drain  waters,  sometimes  showing 
a  heavy  depletion  of  the  land  by  the  leaching-out  of  this  im- 
portant plant  food. 

It  has  been  computed  by  John  Murray,  as  quoted  by  Rus- 
sell,1 that  the  volume  of  water  flowing  into  the  sea  in  one 
year,  including  all  the  land  areas  of  the  earth,  is  about  6524 
cubic  miles.  From  the  average  composition  of  river  waters 
as  given  above,  it  would  follow  that  nearly  five  billions  (4,975,- 
117,588)  of  tons  of  mineral  matter  are  annually  carried  away 
in  solution  from  the  land  into  the  sea.  The  amount  of  sedi- 
ment carried  at  the  same  time  is  many  times  greater;  in  the 
case  of  the  Mississippi  river,  it  is  more  than  five  times  the 
amount  of  the  matter  carried  in  solution. 

Comparison  of  the  river  waters  among  themselves  shows 
less  of  any  consistent  relation  to  climatic  conditions  than  might 
have  been  anticipated.  The  waters  of  the  arctic  streams 

1  Rivers  of  North  America,  p.  80. 


THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION.         35 

Yukon  and  Dwina  show  wider  differences  than  any  two  other 
waters  in  the  list,  unless  it  be  the  St.  Lawrence,  another 
northern  stream.  The  Missouri  and  Rio  Grande  show  by 
their  high  content  of  soda,  chlorin  and  sulfuric  acid  their 
origin  in  arid  climates,  where  alkali  lands  prevail.  The  water 
of  the  Nile  is  here  represented  by  two  analyses,1  one  showing 
the  season  when  the  water  is  "  red  "  and  of  high  fertilizing 
quality  because  of  the  sediment  it  brings  down  from  the 
mountains  of  Abyssinia ;  the  other  the  "  green  "  and  relatively 
clear  water  which  comes  from  the  great  lakes  and  through  the 
"  sudd  "  or  grassy  swamp  region  near  the  junction  of  the 
Gazelle  river  with  the  Nile.  Of  the  analyses  given  of  the 
Mississippi  river  water,  the  first  represents  the  average  of  a 
full  year's  observations  made  weekly  under  the  auspices  of  the 
New  Orleans  Commission  on  Sewerage  and  Drainage,  by  J. 
L.  Porter.  The  fourth  is  an  analysis  made  of  water  taken  at 
the  same  point  in  May,  1905  ;  the  analysis  having  been  made  in 
full  by  Mr.  Stone,  of  the  Reclamation  Service  of  the  U.  S. 
Geol.  Survey,  the  direct  determination  of  potash  and  soda 
being  in  this  case  included.  As  will  be  seen,  and  might  be  ex- 
pected, the  average  of  the  Mississippi  water  corresponds  quite 
nearly  to  that  of  nineteen  of  the  world's  great  rivers  as  given 
by  Murray.  The  very  great  variation  in  the  content  of  sul- 
fates  is  evidently  due  to  the  occasional  heavy  influx  of  the 
gypseous  waters  of  the  Washita  and  Red  rivers  when  in  flood ; 
while  the  minimum  content  (in  January)  agrees  almost  pre- 
cisely with  the  general  average.  Murray's  table  would  hardly 
be  changed  if  these  analyses  of  Mississippi  water  were  incor- 
porated therein,  owing  doubtless  to  the  large  and  varied 
drainage  area  of  the  great  river. 

Sea    Water. — The    nature   of    the   substances    permanently 

1  The  correctness  of  Letheby's  analyses  has  been  disputed,  partly  because  of  their 
disagreement  with  former  analyses  in  the  very  high  amount  of  lime,  partly  because 
of  the  high  potash-content  in  the  Low-Nile  water.  The  lime  content  is,  however, 
confirmed  by  the  partial  analyses  made  by  Matheyin  1887,  which  gives  an  average 
of  44.1  for  the  year,  while  the  older  analyses,  made  in  Europe,  of  transported  water 
gave  only  half  as  much.  Letheby  working  on  the  spot  was  doubtless  more  nearly 
right  in  this  respect.  His  figure  for  potash  in  the  "  Low-Nile  "  water  agrees  with 
former  determinations,  but  that  in  the  "  High-Nile  "  is  approached  only  by  that  in 
the  Dwina  water.  It  may  be  suspected  that  the  soda  is  too  low  and  potash  too 
high  in  this  analysis. 


26  SOILS. 

leached  out  is  also  seen  by  considering  the  composition  of  sea 
water,  since  the  ocean  is  the  final  reservoir  for  all  the  leaching-s 
of  the  land.  It  might  be  objected  that  the  ocean  may  have 
received  its  salts  from  other  sources ;  but  this  objection  is  over- 
borne by  the  fact  that  substantially  the  same  salts  are  found  in 
landlocked  lakes,  in  which,  as  they  have  no  outflow,  the  leach- 
ings  of  the  adjacent  regions  are  perforce,  as  a  rule,  the  only 
possible  source  of  the  salts.  It  is  true  that  the  nature  of  the 
salts  differs  somewhat  in  different  lakes,  as  might  be  expected ; 
but  a  general  statement  of  that  nature  will,  after  all,  be  the 
same  as  that  made  in  regard  to  sea-water.  The  following 
table  of  the  average  composition  of  sea-water,  according  to 
Regnault,  illustrates  these  facts. 


MEAN  COMPOSITION  OF  SEA-WATER. 


Sodium  Chlorid  (common  salt) 2.700 

Potassium  chlorid 070 

Calcium  sulfate  (gypsum)    140 

Magnesium  sulfate  (Epsom  salt) .230 

Magnesium  chlorid  (bittern)    360 

Magnesium  bromid 002 

Calcium  carbonate  (limestone) 003 

Water  (and  loss  in  analysis)   96.495 


100.000 


The  average  saline  contents  of  sea-water  would  thus  be 

3.505  per  cent.     In  twenty-one  determinations  of  the  saline 
contents  of  the  Atlantic  Ocean,  the  percentage  ranged  from 

3.506  to  3.710  per  cent.     Of  this  mineral  residue,  common 
salt  constitutes  from  about  75  to  over  80  per  cent. 

We  see  that  most  prominent  among  the  ingredients  mentioned  here 
is  common  salt  (sodium  chlorid),  which  forms  nearly  four-fifths  of  the 
total  solid  contents.  Next  in  quantity  are  the  compounds  of  magnesium, 
viz.  Epsom  salt  and  bittern,  with  a  very  small  amount  of  the  bromin 
compound.  Next  come  the  compounds  of  calcium  (lime),  of  which 
gypsum  is  the  more  abundant,  while  the  carbonate,  so  abundant  on  the 
land  surface  in  the  various  forms  of  limestone,  is  present  in  minute 
amounts  only,  yet  enough  to  supply  the  substance  needed  for  the  shells 


THE  CHEMICAL  PROCESSES  OF  SOIL  FORMATION.        37 

of  shellfish,  corals,  etc.  Least  in  amount  of  the  metallic  elements 
mentioned  is  potassium.  Calculating  the  total  amounts  of  chlorin,  we 
find  that  it  exceeds  in  weight  any  one  other  element  present  in  the  salts 
of  sea-water,  being  two-sevenths  of  the  whole  solids. 

Substantially  the  same  result,  with  variations  due  to  local  causes,  as 
exemplified  in  the  varying  composition  of  river  and  drain  waters,  is 
obtained  when  we  consider  the  saline  ingredients  of  lakes  having  no 
outlet,  and  in  which  therefore,  the  leachings  of  the  tributary  land  area 
have  accumulated  for  ages.  The  Great  Salt  Lake  of  Utah,  the  land- 
locked lakes  of  the  Nevada  basin,  of  California,  Oregon,  and  of  the 
deserts  of  Asia,  Africa,  and  Australia,  all  tell  the  same  tale,  which  may 
be  summarized  in  the  statement  that  the  chlorids  of  sodium  and 
magnesium,  and  the  sulfates  of  sodium,  magnesium  and  calcium  con- 
stitute the  bulk  of  the  leachings  of  the  land ;  while  of  other  substances 
potassium  alone  is  present  in  relatively  considerable  amount. 

While  the  above  analysis  shows  the  ingredients  of  sea-water  so  far  as 
they  can  at  present  be  directly  determined  by  chemical  analysis,  yet  the 
presence  of  many  others  is  demonstrable,  directly  or  indirectly,  from 
various  sources.  One  is,  the  mother-waters  from  the  making  of  sea-salt, 
in  which  such  substances  accumulate  so  as  to  become  ascertainable  by 
chemical  means,  and  even  become  industrially  available  in  the  cases  of 
potash  and  bromin.  Another  is  the  ash  of  seaweeds,  which  is  in- 
disputably derived  from  the  sea-water,  and  contains,  among  other  sub- 
stances not  directly  demonstrable  in  the  original  water,  notable  quantities 
of  iodin  (of  which  this  ash  is  a  commercial  source),  iron,  manganese, 
and  phosphoric  acid.  Again,  the  copper  sheathing  of  vessels,  as  it  is 
gradually  corroded,  becomes  more  or  less  rich  in  silver,  manifestly 
thrown  down  from  the  sea-water,  and  the  silver  so  obtained  is  associated 
with  minute  amounts  of  gold.  Copper,  lithium,  and  fluorin  likewise 
have  been  found  in  sea  water ;  and  it  is  probable  that  close  search 
would  detect  very  many  of  the  other  chemical  elements  as  ordinary  in- 
gredients in  minute  amounts.  This  is  what  must  be  expected  from  the 
fact  that  few  mineral  substances  known  to  us  are  entirely  insoluble  in 
pure  water,  and  still  fewer  in  water  charged  with  carbonic  acid.  The 
latter  is  always  present  in  sea-water  and  holds  the  lime  carbonate  in 
solution ;  on  evaporation  or  boiling,  this  substance  is  the  first  to  be 
precipitated  ;  and  thin  sheets  of  limestone  from  this  source  are  com- 
monly found  at  the  base  of  rock-salt  beds,  which,  themselves,  are 
evidently  the  result  of  the  evaporation  of  segregated  bodies  of  sea-water 
in  past  geological  ages. 


28  SOILS. 

Summing  tip  the  facts  concerning  the  water  of  the  sea  and 
of  landlocked  lakes,  with  reference  to  the  ingredients  of  soils 
needful  for  the  nutrition  of  plants,  it  appears  that  the  rock-in- 
gredients leached  out  in  the  largest  amounts  (lime  alone  ex- 
cepted)  are  those  of  which  the  smallest  quantities  only  are  re- 
quired by  most  plants;  while  of  those  specially  needful  for 
plant  nutrition,  only  potash  is  removed  in  practically  apprecia- 
ble amounts  by  the  stream  drainage. 

Result  of  insufficient  Rainfall;  Alkali  Soils. — When  the  rain- 
fall is  either  in  total  quantity,  or  in  consequence  of  its  distribu- 
tion in  time,  insufficient  to  effect  this  leaching,  the  substances 
that  otherwise  would  have  passed  into  the  drainage  and  the 
sea  are  wholly  or  partially  retained  in  the  soil;  and  when  the 
rainfall  deficiency  exceeds  a  certain  point,  the  salts  thus  re- 
tained may  become  apparent  on  the  surface  in  the  form  of 
saline  efflorescences,  or  as  it  is  usually  termed  in  North  Amer- 
ica, "  alkali."  1  Their  continued  presence  modifies  in  various 
ways  the  process  of  soil  formation  and  the  nature  of  the  soils 
as  compared  with  those  of  regions  of  abundant  rainfall  ("  hu- 
mid climates  ")  ;  one  of  the  most  prominent  and  important  re- 
sults being  that,  besides  the  easily  soluble  salts  mentioned 
above,  the  carbonate  of  lime  formed  in  the  process  of  decom- 
position is  also  retained,  and  imparts  to  the  soils  of  regions  of 
deficient  rainfall  ("arid  climates")  the  almost  invariable 
character  of  calcareous  lands.  There  is  thus  in  the  United 
States  a  marked  and  practically  very  important  contrast  be- 
tween the  soils  of  the  arid  region  west  of  the  Rocky  Moun- 
tains and  those  of  the  "  humid  "  region  between  the  immediate 
valley  of  the  Mississippi  and  the  Atlantic  coast.  These  differ- 
ences and  their  practical  bearings  can  be  best  discussed  after 
first  considering  more  in  detail  the  chemical  decomposition  of 
the  several  soil-forming  minerals. 

1  In  some  cases  the  soluble  salts  originate  in  rocks  impregnated  with  salts  from 
marine  lagoons  or  landlocked  lakes,  or  directly  from  their  evaporation  residues. 
But  this  is  the  execution  rather  than  the  rule. 


CHAPTER  III. 

THE  MAJOR  SOIL-FORMING  MINERALS. 

Since  the  several  stratified  rocks,  such  as  sandstones, 
shales,  claystones,  clays,  limestones,  etc.,  are  themselves 
but  the  outcome  of  the  same  disintegrating  and  decom- 
posing influences  upon  the  crystalline  rocks  by  which 
soils  are  now  formed,  we  must  study  the  action  of  these  influ- 
ences upon  the  minerals  composing-  the  latter  rocks  in  order  to 
gain  a  comprehensive  understanding  of  the  subject.  While 
the  number  of  different  minerals  known  to  science  is  very 
large,  such  study  need  not  go  beyond  a  small  number  of  the 
chiefly  important,  rock-forming  species  which  are  so  generally 
distributed  as  to  require  consideration  in  this  connection. 
These  minerals  are  the  following :  Quartz  and  its  varieties ; 
the  several  feldspars ;  hornblende  and  augite ;  the  micas ;  talc 
and  serpentine.  Calcite,  gypsum  and  dolomite,  though  not 
contained  in  the  older  rocks,  must  be  considered  because  of 
their  forming  large  rock  deposits  by  themselves;  and  zeolites 
require  mention  because,  though  rarely  forming  a  large  pro- 
portion of  rocks,  they  are  of  special  importance  as  soil  ingre- 
dients. 

Quartz  and  the  minerals  allied  to  it  consist  essentially  of 
dioxid  of  silicon,  usually  without  (quartz  proper)  but  partly 
also  with  water  in  combination  (opal  and  its  varieties).  Sili- 
con is  next  to  oxygen  the  most  abundant  element  found  on  the 
earth's  surface.  It  occurs  largely  in  the  various  forms  of 
quartz,  alone,  or  as  one  ingredient  of  compound  rock-masses; 
the  rest,  in  combination  (as  silica)  with  various  metallic  oxids. 
forms  the  important  group  of  silicate  minerals,  constituting 
the  bulk  of  most  rocks. 

Quartz  occurs  frequently  in  crystals  (rock  crvstal ;  six-sided 
prisms  terminated  by  six-sided  pyramids),  clear  or  variously 
colored ;  but  more  abundantly  as  quartz  rock  or  quartzite,  read- 
ily known  by  its  hardness,  so  as  to  strike  fire  with  steel,  and 

29 


30  SOILS. 

by  its  glass-like,  irregular  fracture.  Besides  the  crystalline 
quartz  rock  we  find  close-grained  and  at  least  partly  non-crys- 
talline varieties,  such  as  hornstone  and  flint.  Sandstones  most 
commonly  consist  of  grains  of  quartz  cemented  by  some  other 
mineral,  or  by  silica  itself;  in  the  latter  case  the  siliceous  sand- 
stone frequently  passes  insensibly  into  true  quartzite.  The 
loose  sand  so  well  known  to  common  life  is  prevalently  com- 
posed of  quartz  grains,  whose  hardness  and  resistance  to 
weathering  enables  them  to  survive  longest  the  soil-forming 
agencies. 

Quartz  and  its  allied  rocks — jasper,  hornstone,  siliceous 
schist,  etc.,  are  all,  as  already  stated,  acted  on  with  difficulty 
by  the  "  weathering  "  agencies.  Crystalline  quartz  rock  may 
be  considered  as  practically  refractory  against  all  but  the 
mechanical  agencies,  and  hence  remains  in  the  form  of  sand 
and  gravel,  more  or  less  rounded  by  attrition,  as  a  prominent 
component  of  most  soils ;  sometimes  to  the  extent  of  over  92 
per  cent,  even  in  soils  highly  esteemed  in  cultivation,  especially 
in  the  arid  region.  Such  soils  are  mostly  the  result  of  the  dis- 
integration of  sandstones,  the  cement  of  which  has  been  dis- 
solved out  in  the  course  of  weathering;  or  they  may  be  derived 
directly  from  geological  deposits  of  more  or  less  loose  and  un- 
consolidated  sand.  Among  crystalline  rocks,  granites,  gneiss 
and  mica-schists  are  those  most  usually  concerned  in  the  form- 
ation of  sandy  soils;  since  in  common  parlance,  quartz  is  un- 
derstood to  be  the  substance  of  the  sand  unless  otherwise  stated. 
The  exceptions  are  especially  important  in  the  regions  of  de- 
ficient rainfall. 

But  while  crystalline  quartz  is  practically  insoluble  in  all 
natural  solvents,  the  same  is  not  true  of  the  jaspers  and  horn- 
stones.  These  consist  of  a  mixture  of  crystalline  and  amor- 
phous (non-crystalline)  silica,  which  is  more  readily  soluble 
than  the  crystalline,  and  is  attacked  by  many  natural  waters, 
especially  by  those  containing  even  very  small  amounts  of  the 
carbonates  of  potash  or  soda.  We  thus  often  find  that  horn- 
stone  and  jasper  pebbles  buried  in  the  soil,  while  still  hard  in- 
ternally, have  externally  been  converted  into  a  friable,  almost 
chalky  substance,  consisting  of  crystalline  quartz  from  which 
the  cementing  amorphous  silex  has  been  removed  by  the  soil 
water.  In  the  course  of  time  such  pebbles  may  be  completely 


THE  MAJOR  SOIL-FORMING  MINERALS.  31 

destroyed  by  this  process,  so  as  to  be  light  and  chalky  through- 
out, and  readily  crushed  in  tillage.  The  change  is  the  more 
striking  when,  as  frequently  happens,  the  hornstone  pebble  is 
traversed  by  small  veins  of  crystalline  quartz,  which  remain  as 
a  skeleton. 

Solubility  of  Silica  in  Water. — It  is  easily  shown  experimen- 
tally that  the  compound  of  silica  with  water  (hydrate)  is  under 
certain  conditions  readily  soluble  not  only  in  pure  water,  but 
also  in  such  as  contains  carbonic  acid.  It  thus  occurs  in  nearly 
all  spring  and  well  waters ;  some  hot  springs  deposit  large 
masses  of  it  (sinter)  ;  and  geological  evidence  clearly  demon- 
strates that  quartz  veins  have  as  rule  been  formed  from  water- 
solutions  of  silica. 

That  silica  in  its  soluble  form  circulates  freely  in  the  soil 
water,  is  abundantly  evident  from  the  large  amounts  of  it 
which  are  secreted  on  the  outside  of  the  stems  of  grasses,  horse- 
tail rushes  and  other  plants,  imparting  a  gritty  roughness  to 
their  outer  surface.  In  the  case  of  the  giant  bamboo  grass  of 
Asia,  the  silica  accumulated  on  the  outside  of  the  joints  forms 
a  hard  sheath  of  considerable  thickness,  known  to  commerce 
as  tabashir. 

That  among  the  first  products  of  rock  decomposition  we 
often  find  small  amounts  of  the  silicates  of  the  alkalies  (potash 
and  soda)  has  already  been  mentioned.  It  cannot  be  doubted 
that  the  same  continues  to  be  formed  in  soil  containing  the 
proper  minerals ;  and  there  they  also  take  part  in  the  formation 
of  the  easily  decomposable  hydrous  silicates  designated  as 
zeolites,  which  are  largely  instrumental  in  retaining  the  "  re- 
serve "  of  mineral  plant-food  in  soils. 

SILICATE    MINERALS. 

Silica  occurs  in  nature  combined  with  the  oxids  of  most 
metals,  forming  silicates ;  but  most  abundantly  with  the  earths 
(lime,  magnesia,  alumina)  and  alkalies  (potash  and  soda). 
These  compounds  are  the  most  important  in  soil  formation; 
and  among  them  the  following  are  the  chief: 

The  Feldspars,  which  may  be  defined  as  compounds  of 
silicates  of  potash,  soda  or  lime  (either  or  all)  with  silicate  of 
alumina.  They  are  prominent  ingredients  of  most  crystalline 


32  SOILS. 

rocks;  potash  feldspar  (orthoclase)  with  quartz  and  mica  forms 
granite  and  gneiss;  feldspars  containing  soda  and  lime  (either 
or  both)  form  part  of  many  other  crystalline  rocks,  such  as 
basalt,  diabase,  diorite,  gabbro  and  most  lavas.  The  feldspars 
are  decomposed  by  weathering  rather  readily,  and  are  import- 
ant in  being  the  chief  source  of  clays  as  well  as  of  potash  in 
soils.  When  acted  upon  by  carbonated  water,  the  bases 
potash,  soda,  and  lime  or  carbonates,  the  silica  being  mostly 
displaced;  while  the  silicate  of  alumina  takes  up  water  and 
forms  kaolinite,  the  essential  basis  of  clays,  and  one  of  the 
most  important  constituents  of  soils;  imparting  to  them  the 
necessary  firmness  and  cohesion,  together  with  other  important 
physical  properties,  discussed  more  in  detail  hereafter. 

While  thus  on  the  one  hand  feldspars  are  the  source  of  clay, 
on  the  other  they  supply  one  of  the  most  essential  ingredients 
of  plant  food,  viz.  potash ;  which  is  first  dissolved  by  the  water 
in  the  forms  of  carbonate  and  silicate,  but  in  most  cases  soon 
becomes  fixed  in  the  soil  by  forming  more  complex  (zeolitic) 
combinations.  The  soda  not  being  retained  by  the  soil  as 
strongly  as  is  potash  is  washed  through  into  the  country  drain- 
age; while  if  lime  is  present,  it  mostly  remains  in  the  form  of 
the  carbonate. 

Orthoclase  feldspar  contains  nearly  17%  of  potash; 
Leucite,  a  related  mineral  occurring  in  some  lavas,  contains 
21.5%.  The  other  feldspars  contain  only  a  few  per  cent, 
sometimes  none. 

Other  silicate  minerals,  so  far  as  they  contain  the  same 
bases,  are  acted  upon  similarly  to  the  feldspars. 

In  the  decomposition  of  the  feldspars  by  carbonated  water,  the  com- 
pounds of  potash  and  soda  so  formed  are  soluble  in  water,  those  of 
lime  and  magnesia  are  insoluble  or  nearly  so.  Hence  pure  clays  can 
be  formed  only  in  the  decomposition  of  the  potash-  and  soda-feldspars 
(orthoclase,  albite)  while  in  the  case  of  lime  feldspar  (labradorite)  and 
the  mixed  feldspars  (plagioclase,  anorthite)  calcareous  clays  (marls) 
are  the  result.  Lime  feldspar  resists  decomposition  more  tenaciously 
than  do  those  containing  large  proportions  of  the  strong  bases  potash 
and  soda ;  potash  feldspar  especially  is  attacked  most  readily,  and  is 
the  main  source  of  the  formation  of  the  valuable  deposits  of  porcelain 
earth  or  kaolin,  which  is  essentially  a  mixture  of  kaolinite  with  fine  silex 
and  more  or  less  of  undecomposed  feldspar,  and  is  of  a  chalky  texture. 


THE  MAJOR  SOIL-FORMING  MINERALS.  33 

Formation  of  Clays. — When  instead  of  remaining  in  place, 
this  kaolin  is  washed  away  and  triturated  in  the  transportation 
by  water,  it  is  partially  changed  from  its  original  chalky  con- 
dition to  that  plastic  and  adhesive  form  which  is  the  character- 
istic ingredient  of  all  clays.  The  remarkable  properties  of  this 
substance  and  the  part  it  plays  in  the  physical  constitution  of 
soils,  will  be  discussed  in  another  chapter.  Its  lightness  and 
extreme  fineness  of  grain  (if  grain  it  can  be  called)  cause  it  to 
be  carried  farther  on  by  the  streams  than  any  other  portion  of 
the  products  of  rock-decomposition  save  those  actually  in 
solution ;  it  can  therefore  be  deposited  only  in  water  that  is 
almost  or  quite  still  (as  in  swamps)  so  long  as  the  latter  is 
fresh.  So  soon  however  as  brackish  or  salt  water  is  en- 
countered, clay  promptly  gathers  into  floccules  (''  floccu- 
lates"), and  thus  enveloping  the  finest-grained  silts  that  may 
have  been  carried  along  with  it,  it  quickly  settles  down,  form- 
ing the  "  mud  banks  "  and  heavy  clay  soils  that  are  so  char- 
acteristic of  the  lower  deltas  of  rivers,  as  well  as  of  swamps 
formed  by  the  backwater  or  overflow  of  the  same. 

When  instead  of  potash  feldspar  alone,  the  lime-  or  soda- 
lime  feldspars  are  also  concerned  in  the  decomposition  process, 
the  resulting  clay  soils  will  be  more  or  less  calcareous,  while 
the  soda,  as  stated  above,  is  for  the  greater  part  leached  out 
permanently. 

Hornblende  (Amphibole)  and  Pyroxene  (Augite).  These 
are  two  very  widely  diffused  minerals,  differing  but  little  in 
composition  though  somewhat  differently  crystallized,  mostly 
in  short  columnar  forms.  The  typical  and  most  abundant 
varieties  of  these  minerals  appear  black  to  the  eye,  though  in 
thin  sections  they  are  bottle-green ;  they  form  the  black  in- 
gredient of  most  rocks. 

The  color  is  due  to  ferroso-ferric  (magnetic)  oxid  of  iron  ;  the  mineral 
as  a  whole  may  be  considered  as  a  silicate  of  lime,  magnesia,  alumina 
and  iron,  varying  greatly  in  their  absolute  proportions  ;  alumina  and 
iron  being  sometimes  almost  absent.  When  iron  is  lacking  the  mineral 
may  be  almost  white  (tremolite,  asbestos),  and  its  weathering  is  then 
much  retarded,  since  the  oxygen  of  the  air  cannot  take  part  in  the  pro- 
cess of  disintegration. 

The  black  variety  of  hornblende  is  not  only  the  most  abun- 
3 


34 


SOILS. 


dant  as  a  rock-ingredient,  but  it  also  the  one  most  easily  de- 
composed and  therefore  most  commonly  concerned  in  soil 
formation.  The  black  hornblende  owes  its  easy  decomposi- 
tion under  the  atmospheric  influences  to  two,  properties;  one, 
its  easy  cleavage,  whereby  cracks  are  readily  formed  and  ex- 
tended by  the  agencies  already  mentioned  (pp.  1-3).  The  other 
is  its  large  content  of  ferrous  silicate  (silicate  of  iron  pro- 
toxide), whereby  it  is  liable  to  attack  from  atmospheric  oxy- 
gen; the  latter  forms  ferric  hydrate  (iron  rust)  out  of  the  pro- 
toxide, thus  causing  an  increase  of  bulk  which  tends  to  split  the 
masses  of  the  mineral  in  several  directions,  while  the  silex  is 
set  free.  At  the  same  time  the  carbonic  acid  of  the  air  con- 
verts the  silicate  of  lime  and  magnesia,  which  forms  the  rest 
of  the  mineral,  into  carbonates;  and  the  alumina  present  forms 
kaolinite,  as  in  the  case  of  the  feldspars.  There  is  thus 
formed  from  this  mineral,  when  alone,  a  strongly  rust-colored, 
more  or  less  calcareous  and  magnesian  clay,  constituting  the 
material  for  rather  light-textured  "  red  "  soils.  In  most 
cases  however  the  hornblende  is  associated  in  the  rock  itself 
with  the  several  feldspars,  (mostly  lime-  and  soda-lime  feld- 
spars) as  well  as  with  more  or  less  quartz.  The  rust-colored 
soils  are  therefore  most  commonly  the  joint  result  of  the 
weathering  of  these  several  minerals.  This  is  well  exempli- 
fied in  the  case  of  the  "  red  "  soils  formed  from  the  so-called 
granites  and  slates  of  the  western  slope  of  the  Sierra  Nevada 
of  California. 

Pyroxene  or  Augite  so  nearly  resembles  hornblende  in  its 
chemical  composition  and  crystalline  form,  that  what  is  said  of 
the  latter  may  be  considered  as  applying  to  augite  also.  Owing 
however  to  the  absence  of  any  prominent  tendency  to  cleavage, 
the  smooth  crystals  of  this  mineral  are  attacked  much  less 
readily  than  is  hornblende,  so  that  we  often  find  them  as 
"  black  gravel  "  in  the  soils  formed  from  rocks  containing 
it.  Such  soils  are  particularly  abundant  and  important  in  the 
region  covered  by  the  great  sheet  of  eruptive  rocks  (basalts, 
so-called)  in  the  Pacific  Northwest,  and  on  the  plateau  of 
South  Central  India  (the  Deccan),  and  result  likewise  from 
the  decomposition  of  the  black  lavas  of  volcanoes ;  thus  in  the 
Hawaiian  islands,  and  in  the  Andes  of  Peru  and  Chile. 

Both  hornblende  and  augite  being  either  free  from,  or  de- 


THE  MAJOR  SOIL-FORMING  MINERALS.  35 

ficient  in  potash,  of  course  the  soils  formed  from  them  are  apt 
to  lack  an  adequate  supply  of  this  substance  for  plant  use. 
This  is  markedly  true  of  hornblende  schist  or  amphibolite 
rocks. 

Mica,  commonly  known  as  isinglass,  is  so  conspicuous 
wherever  it  occurs  that  it  is  more  readily  recognized  than  any 
other  mineral.  It  occurs  in  glittering  scales  in  soils  and 
sands,  and  in  rocks  it  sometimes  forms  sheets  of  sufficient  size 
to  supply  the  small  panes  for  the  doors  of  stoves,  lamp 
chimneys,  etc.,  which  being  flexible  are  not  liable  to  break,  but 
only  gradually  scale  into  very  thin  films,  into  which  it  can  also 
be  split  by  hand.  When  white,  (muscovite,  phlogopite)  its 
scales  are  sometimes  mistaken  for  silver  by  mine  prospectors; 
when  yellow,  for  gold ;  but  their  extreme  lightness  should 
soon  remove  these  delusions.  The  composition  of  mica  is  not 
widely  different  from  that  of  the  two  preceding  minerals ;  like 
these  it  sometimes  contains  much  iron,  and  is  then  dark  bottle- 
green  (biotite)  ;  this  variety  in  weathering  becomes  bright 
yellow,  and  soon  disintegrates. 

This  mineral  is  so  abundant  an  ingredient  of  many  rocks  and 
soils,  that  one  naturally  looks  for  it  to  play  some  definite  or  im- 
portant part  in  soil  formation.  By  its  ready  cleavage  it  favors 
the  disintegration  of  rocks ;  but  it  seems  that  owing  to  the  ex- 
tremely slow  weathering  of  its  smooth,  shining  cleavage  sur- 
faces, it  exerts  no  notable  effect  upon  the  chemical  composi- 
tion of  the  soil,  although,  owing  to  its  peculiar  character  of 
fine  scales,  it  sometimes  adds  not  immaterially  to  the  facility 
of  tillage  in  otherwise  somewhat  intractable  soils.  So  far  as 
is  known  at  present,  its  presence  or  absence  does  not  constitute, 
in  itself,  any  definite  cause  or  indication  of  the  quality  of  any 
soil.  It  may  nevertheless  be  said  that  the  rock  in  which  it 
usually  occurs  most  abundantly — mica-schist,  a  mixture  of 
mica  and  quartz — is  known  to  form,  as  a  rule,  lands  of  poor 
quality.  On  the  other  hand,  the  soils  derived  from  granites 
and  gneisses,  even  when  rich  in  mica,  are  usually  excellent,  on 
account  of  their  content  of  feldspars,  and  frequently  of  other 
associated  minerals. 

Hydoniica  differs  from  the  preceding  mainly  in  containing 
a  larger  proportion  of  combined  water;  but  it  hardly  de- 


36  SOILS. 

composes  more  readily,  and  the  rocks  in  which  it  mainly  occurs 
(hydromica  schists)  are  refractory  to  weathering,  and  in  any 
case  do  not  yield  soils  of  any  fertility,  the  mineral  being  as- 
sociated simply  with  quartz. 

Chlorite,  essentially  a  silicate  of  alumina  and  iron,  somewhat 
resembles  mica  but  is  deep  green  or  black,  in  small  scales.  It 
forms  part  of  certain  rocks  (chlorite  schists),  which  greatly 
resemble  the  hornblende  schists,  but  are  usually  inferior  to  the 
latter  as  soil-formers,  containing  but  little  of  any  direct  value  to 
plant  life. 

Talc  and  Serpentine,  Hydrous  silicates  of  magnesia,  are 
extensive  rock-materials  in  some  regions,  and  as  such  require 
mention  as  soil-formers  also.  Serpentine  usually  forms  black- 
ish-green rock-masses,  that  although  soft  disintegrate  very 
slowly  in  the  absence  of  definite  structure,  and  are  attacked 
with  some  energy  only  when  charged — as  is  frequently  the 
case — with  ferrous  oxide.  The  conversion  of  this  into  ferric 
hydrate,  so  common  in  nature,  here  also  serves  as  the  point  of 
attack  on  a  rock  otherwise  very  stable;  causing  it  to  crumble, 
even  though  slowly. 

Talc  (the  true  "soapstone")  being  usually  free  from  iron, 
would  be  even  more  slow  than  serpentine  to  yield  to  weather- 
ing, but  that  its  extreme  softness  and  ready  cleavage  greatly 
facilitate  its  abrasion.  Thus  talc  schist,  which  is  usually  a 
mixture  of  talc  with  more  or  less  quartz,  undergoes  mechanical 
disintegration  quite  readily. 

But  the  soils  formed  from  either  serpentine  or  talcose  rocks 
are  almost  always  very  poor  in  plant  food,  and  sometimes 
totally  sterile.  Magnesia,  though  an  indispensable  ingredient 
of  plant  food,  is  rarely  deficient  in  soils  and  unlike  lime  does 
not  influence  in  any  sensible  degree  the  process  of  soil  forma- 
tion. Magnesian  rocks  as  a  whole  are  practically  found  to  be 
not  specially  desirable  soil-formers,  even  in  the  form  of 
magnesian  limestones.  They  do  not  even,  as  a  rule,  contain 
as  many  useful  accessory  minerals  as  are  commonly  found  in 
limestones.  Moreover,  an  excess  of  magnesia  over  lime  is 
injurious  to  most  crops,  as  is  shown  later  (chapt.  18). 

The  Zeolites. — Zeolites  may  be  defined  as  hydro-silicates 
containing  as  bases  chiefly  lime  and  alumina,  commonly  to- 


THE  MAJOR  SOIL-FORMING  MINERALS.  37 

gether  with  more  or  less  of  potash  and  soda,  more  rarely 
magnesia  and  baryta.  The  water  is  easily  expelled  by  heat- 
ing, but  is  present  in  the  basic  form,  not  merely  as  water  of 
crystallization.  All  zeolites  are  readily  decomposed  by  chlor- 
hydric  and  other  stronger  acids. 

The  zeolites  proper  are  not  original  rock  ingredients,  but  are  formed 
in  the  course  of  rock  decomposition  by  atmospheric  agencies,  heated 
water,  and  other  processes  not  fully  understood.  They  are  therefore 
usually  found  in  the  cavities  and  crevices  of  rocks  that  have  been  sub- 
ject to  the  influence  of  atmospheric  or  thermal  waters,  most  frequently 
in  eruptive  rocks,  particularly  in  the  vesicular  cavities  characterizing 
what  is  known  as  amygdaloids.  They  are  also  found  in  the  crevices  of 
sandstones  and  shales  percolated  by  water,  as  well  as  in  nodules  of 
infiltration  (geodes),  in  which  they  are  frequently  associated  with  quartz. 
Those  found  in  the  cavities  of  rocks  are  usually  well  crystallized  wherever 
room  is  afforded,  and  are  readily  recognized  by  their  crystalline  form; 
they  are  mostly  colorless,  sometimes  yellow  or  reddish. 

Exchange  of  bases  in  Zeolites. — Although  zeolites  rarely 
form  a  large  proportion  of  rock  masses  and  therefore  do  not 
enter  directly  into  the  soil  minerals  to  any  great  extent,  their 
interest  in  connection  with  soil-formation  is  very  great,  because 
of  the  continuation,  within  the  soil,  of  the  same  processes  that 
bring  about  their  formation  in  rocks.  Under  the  conditions 
existing  in  soils  they  will  naturally  rarely  form  crystals,  but 
will  appear  in  the  pulverulent  or  gelatinous  form,  leaving  the 
zeolitic  nature  of  the  material  to  be  inferred  from  its  chemical 
behavior.  Among  these  characters  the  ready  decomposability 
by  acids  has  already  been  mentioned  ;  another  of  special  import- 
ance in  the  economy  of  soils  is  the  fact  that  when  a  pulverized 
zeolite  is  subjected  to  the  action  of  a  solution  containing  either 
of  the  stronger  bases  usually  present  (potash,  soda  or  lime), 
such  base  or  bases  will  be  partially  or  wholly  taken  up  by  the 
zeolitic  powder,  while  corresponding  amounts  of  the  bases 
originally  present  will  pass  into  solution. 

Thus  when  a  hydrosilicatc  of  soda  and  alumina  is  digested  with  a 
solution  of  potassic  chlorid  or  sulphate,  the  soda  may  be  partially  or 
wholly  replaced  by  potash,  while  the  corresponding  sodium  salt  passes 
into  solution.  In  the  case  of  zeolites  containing  lime  or  magnesia  or 


38  SOILS. 

both,  the  action  of  potassic  or  sodic  chlorid  will  be  to  partially  replace 
the  lime,  while  calcic  and  magnesic  chlorids  pass  into  solution,  result- 
ing in  the  partial  or  complete  replacement  of  the  lime  by  one  or  the 
other,  or  by  both  bases.  It  is  important  to  note  that,  other  things 
being  equal,  potash  is  usually  absorbed  in  greater  amounts  and  is  held 
more  tenaciously  than  soda.  The  process  may  frequently  be  partially 
or  wholly  reversed  again,  by  subsequent  treatment  with  large  amounts 
of  solutions  of  the  displaced  base  or  bases.  Thus  while  a  solution  of 
potassic  chlorid  may  be  made  to  expel  almost  completely  the  sodium 
present  in  analcite,  subsequent  treatment  with  sodic  chlorid  solution 
will  again  almost  completely  displace  the  potash  before  taken  up.  The 
same  happens  when  the  natural  mineral  potash  leucite,  (see  p.  32)  of  fre- 
quent occurrence  in  certain  lavas,  is  pulverized  and  treated  with  a  sodic 
solution ;  resulting  finally  in  the  production  of  a  mass  corresponding  to 
natural  analcite,  the  sodium  mineral  corresponding  to  leucite. 

In  other  words,  in  any  zeolitic  powder  the  alkaline  or  alkaline 
earth  bases  present  may  be  partially  or  wholly  displaced  by 
digestion  with  an  excess  of  solution  of  any  of  these,  varying 
according  to  the  amount  of  solution  employed,  and  the  length 
of  time  and  temperature  of  action. 

This  characteristic  behavior  of  zeolites  is  exactly  reproduced 
in  soils.  Few  soils  permit  any  saline  solution  to  pass  through 
them  unchanged ;  solutions  of  alkaline  chlorids  filtered  through 
soils  almost  invariably  cause  the  passing  through  of  calcium 
and  magnesium  chlorids,  while  a  part  of  the  alkaline  base  is  re- 
tained ;  and  as  a  matter  of  fact,  we  find  that  this  absorbing 
power  of  soils  for  alkaline  bases  is  more  or  less  directly  pro- 
portional to  the  amount  of  matter  which  may  be  dissolved  or 
decomposed  with  elimination  of  silica,  by  means  of  acids. 

This  absorption  of  bases  from  solutions  by  chemical  fixation  will  be 
farther  discussed  later  on  ;  but  it  should  be  mentioned  here  that  both 
naturally  and  artificially,  rock-masses  are  very  commonly  cemented, 
wholly  or  in  part,  by  zeolitic  material.  Hydraulic  concretes  may  be 
considered  as  sandstones  or  conglomerates  whose  grains  are  cemented  by 
a  zeolitic  cement  consisting  of  silica,  lime  and  alumina,  with  usually  some 
potash  or  soda,  and  of  course  containing  the  basic  water  ;  hence  unaf- 
fected by  the  farther  action  of  the  latter  substance  after  the  time  of  setting 
has  expired, which  varies  somewhat  according  to  the  nature  of  the  material 
used.  That  similar  cements  should  occur  in  natural  sandstones  is  to  be 


THE  MAJOR  SOIL-FORMING  MINERALS.  39 

expected ;  thus  we  find  not  unfrequently  that  certain  sandstones  are 
materially  softened,  and  their  resistance  destroyed,  by  treatment  with 
even  moderately  dilute  acid,  while  silica  and  the  usual  zeolite  bases  pass 
into  solution.  It  is  not  often,  however,  that  zeolitic  material  alone 
cements  the  sandstone ;  it  is  most  frequently  associated  with  siliceous, 
calcareous  and  sometimes  even  with  ferruginous  cementing  material.1 

CALCITE   AND   LIMESTONES. 

Calcite  or  calcareous  spar  is  one  of  the  minerals  most  com- 
monly known  in  the  crystallized  form,  and  is  readily  recognized 
by  its  perfect  cleavage  in  three  directions,  producing  cleavage 
forms  with  smooth,  rhomb-shaped  faces  (rhombohedrons)  ; 
these  are  sometimes  colorless  and  perfectly  transparent,  and 
laid  on  printed  paper  show  the  letters  double.  But  it  may  be 
whitish-opaque,  and  of  various  colors,  which  may  also  be  im- 
parted to  the  limestones  formed  from  it.  It  is  readily  dis- 
tinguished from  quartz,  which  it  sometimes  resembles,  by  its 
cleavage,  its  inferior  hardness,  being  easily  scratched  with  a 
knife;  and  by  its  effervescence  with  acids,  the  latter  being  the 
crucial  test  when  other  marks  are  unavailable,  as  when  it  forms 
soft  granular  masses  or  "  marls."  In  all  cases  it  can  be  recog- 
nized by  its  crystalline  form  under  the  microscope,  even  when 
the  substance  containing  it  has  been  pulverized  in  a  mortar. 
The  great  importance  of  this  compound — calcic  carbonate — 
from  the  agricultural  point  of  view  renders  it  desirable  that 
it,  as  well  as  limestones  as  such,  should  be  recognized,  when 
seen,  by  every  farmer. 

In  mass  the  pure  mineral  constitutes  white  marble  ;  colored  or  vari- 
egated marbles  are  more  or  less  impure  from  the  presence  of  other 
minerals.  Some  compact  limestones  also  are  nearly  pure  ;  and  as  sup- 
plying only  a  single  ingredient  of  plant  food  these  would  not  be  much 
better  soil-formers  than  quartz  or  serpentine.  But  it  is  quite  otherwise 
with  common  limestones  ;  the  mass  of  which,  it  is  true,  is  formed  of 
calc-spar,  but  owing  to  its  origin,  is  in  the  great  majority  of  cases  so  far 
commingled  with  other  matters  of  various  character,  that  limestones  are 

1  A  zeolitic  mass,  at  first  gelatinous  and  then  becoming  granular-crystalline  is 
frequently  observed  oozing  from  the  lower  surface  of  newly  made  concrete  reservoir 
dams:  just  as  we  find  similar  oozes  consolidated  into  natrolite  crusts  in  tin 
crevices  of  natural  sandstones. 


40 

popularly  reputed  to  form  the  very  best  soils.  "  A  limestone  country 
is  a  rich  country  "  is  a  popular  axiom  to  which  there  are,  on  the  whole, 
but  few  exceptions. 

Origin. — Actual  observation  of  what  is  happening  at  the 
present  time,  as  well  as  the  examination  of  the  rock  as  anciently 
formed,  prove  conclusively  that  with  insignificant  exceptions, 
all  limestones  have  been  formed  from  the  framework  and 
shells,  and  to  some  extent  from  the  bones,  of  marine  and 
fresh-water  organisms,  ranging  in  size  from  the  extinct  giants 
of  the  lizard  relationship  to  those  recognizable  only  by  the 
microscope.  Owing  to  the  solubility  of  lime  carbonate  in  car- 
bonated water,  the  organic  forms  have  often  (in  crystalline 
limestones)  been  almost  completely  obliterated  in  some  por- 
tions, but  in  others  are  so  preserved  as  to  prove  undeniably 
the  similarity  of  origin  of  the  whole,  and  that  they  have  been 
formed  in  relatively  shallow  water,  as  they  are  to-day. 

Impure  Limestones  as  Soil-formers. — From  what  has  been 
said  regarding  the  composition  of  sea-water,  it  will  readily  be 
inferred  that  a  pure  deposit  of  any  one  kind  cannot  easily  be 
formed  in  it;  moreover,  the  matter  held  in  mechanical  sus- 
pension everywhere  near  the  coasts  must  very  commonly  be 
included  within  the  calcareous  deposits  formed  off-shore. 
Hence  few  limestones  dissolve  in  acids  without  leaving  a 
residue  of  sand,  clay  and  various  other  substances,  usually 
even  some  organic  matter  not  fully  decomposed;  sometimes 
less  than  half  of  the  mass  is  really  lime  carbonate.  It  is 
obvious  that  when  the  solvent  action  of  carbonated  water  is 
exerted  upon  such  impure  limestones,  a  loose  residue  of  earthy 
matters  will  remain  behind.  It  is  by  this  process  that  a  con- 
siderable proportion  of  the  richest  soils  in  the  world  have  been 
formed,  which  have  given  rise  to  the  popular  maxim  above 
quoted.  They  are  emphatically  "  residual  "  soils ;  sometimes, 
it  is  true,  somewhat  removed,  by  washing-away,  from  their 
point  of  origin,  but  in  many  cases  forming  a  compact  soil- 
layer  on  top  of  the  unchanged  rock,  into  which  there  exists 
every  shade  of  transition.  Striking  examples  of  such  residual 
soils  in  place  are  seen  in  the  black  prairies  of  the  southwestern 
United  States;  they  are  mostly  rather  "stiff"  (clayey),  and 
hence  has  arisen  a  local  popular  error,  to  the  effect  that  clay 


THE  MAJOR  SOIL-FORMING  MINERALS,  41 

or  "  heavy  "  soils  are  always  calcareous.  On  the  other  hand, 
the  blue-grass  region  of  Kentucky,  and  most  of  the  lands  of  the 
arid  regions  are  prominent  examples  of  "  light  "  calcareous 
soils. 

Caves,  Sinkholes,  Stalactites. — Perhaps  the  most  striking  exempli- 
fication of  the  solvent  power  of  carbonated  water  is  seen  in  the  form- 
ation of  limestone  caves.  As  a  matter  of  fact,  the  vast  majority  of  all 
existing  caves  is  found  in  limestone  formations ;  and  such  formations, 
as  will  be  more  fully  discussed  hereafter,  nearly  always  bear  a  luxuriant 
vegetation.  The  water  filtering  through  the  vegetable  mold,  in  which 
carbonic  acid  is  constantly  being  formed,  becomes  charged  with  it,  and 
on  reaching  the  underlying  rock,  dissolves  to  a  corresponding  extent 
the  lime  carbonate  of  which  this  rock  wholly  or  chiefly  consists.  When 
penetrating  crevices  it  soon  enlarges  these,  to  an  extent  proportioned 
to  the  length  of  time  and  the  strength  of  the  solvent ;  and  thus  gradually 
subterranean  passages  or  caves  are  formed,  which  at  first  are  almost 
always  the  bed  of  a  stream,  the  mechanical  action  of  which  accelerates 
the  process  of  enlargement,  until  after  some  time  the  water  is  perhaps 
drained  off  through  some  crevice  to  a  lower  level,  where  the  same  pro- 
cess is  repeated. 

Sometimes  the  ceiling  gives  way,  forming  the  funnel-shaped  "  sink- 
holes" or  "  lime-sinks "  so  familiar  in  some  of  the  Mississippi  Valley 
States.  Sometimes  the  lime  solution  on  reaching  the  ceiling  of  the 
cave,  instead  of  dropping  down,  evaporates  there  and  eventually  forms 
icicle-like  "  stalactites  "  out  of  the  dissolved  substance ;  while  when 
dropping  on  the  floor  and  thus  growing  upwards,  the  corresponding 
formation  is  called  "stalagmite"  These  caves,  subterranean  rivers, 
sinkholes,  natural  bridges  and  tunnels,  etc.,  mostly  owe  their  origin  to 
this  solvent  action  of  carbonated  water  on  limestone  formations.1 

The  same  occurs  on  a  small  scale,  when  calcareous  land  is 
underdrained :  the  lime  carbonate  dissolved  from  the  soil  is 
partially  deposited  in  the  drain  pipes,  which  it  frequently  ob- 
structs. Similarly,  an  impure,  porous  deposit  of  calcareous 
tufa  is  frequently  formed  on  the  surface,  at  the  foot  or  in  rills 

1  T.  M.  Keade  (in  his  treatise  on  Chemical  Denudation  in  Relation  to  Geological 
Time)  calculates  that  143.5  tons  °f  lime  carbonate  are  annually  removed  by  solu- 
tion from  each  square  mile  of  land  in  England  and  Wales,  and  that  the  average 
amount  thus  removed  annually  from  each  square  mile  of  the  earth's  surface 
is  about  fifty  tons. 


42  SOILS. 

of  calcareous  hills.  When  "  hard  "  water,  being  usually  such 
as  contains  lime  carbonate  dissolved  in  carbonic  acid,  is  boiled, 
or  long  exposed  to  the  air,  carbonic  gas  escapes  and  the  lime 
salt  is  deposited  partly  on  the  walls  of  the  kettle,  partly  form- 
ing a  pellicle  on  the  surface  of  the  water. 

Dolomite,  or  bitter  spar,  greatly  resembles  calcite  in  its  as- 
pect and  properties,  although  containing  nearly  half  its  weight 
(47.6%)  of  magnesic,  together  with  calcic  carbonate.  It  is, 
however,  nearly  always  whitish-opaque;  its  crystalline  and 
cleavage  surfaces  are  usually  somewhat  curved;  and  its  effer- 
vescence with  acids  is  much  less  lively  than  in  the  case  of 
calcite.  Like  the  latter  it  often  forms  pure  granular  rock  de- 
posits, frequently  used  instead  of  marble  and  limestone,  and 
under  that  designation.  The  dolomite  rocks,  however,  are 
much  more  subject  to  weathering  than  the  non-magnesian  lime- 
stones, and  it  is  a  curious  fact  that  in  contradistinction  to  the 
limestone  regions  proper,  those  having  strongly  magnesian 
limestones  or  dolomites  as  their  country  rock  are  frequently 
remarkably  sterile.  In  some  portions  of  Europe  dolomite 
areas  are  sandy  deserts,  whose  sand  consists  of  weathered  do- 
lomite, so  pure  as  to  offer  no  adequate  supply  of  mineral  food 
to  plants.  In  the  United  States,  magnesian  limestones  under- 
lie the  "  barrens  "  of  several  States  and  thus  seem  to  justify 
their  European  reputation  of  being  poor  soil-formers.  The 
exact  cause  of  this  difference  is  not  fully  understood,  for  at 
first  sight  it  is  not  clear  why  the  presence  of  the  magnesian 
carbonate  should  interfere  with  the  well-known  beneficial  ef- 
fects of  the  lime  compound.  O.  Loew  and  May  1  and  others 
have,  however,  shown  that  a  certain  excess  of  lime  over  mag- 
nesia in  the  soil  is  necessary  to  prevent  the  injurious  effects 
exerted  by  magnesic  compounds  on  plant  nutrition,  in  the  ab- 
sence of  an  adequate  supply  of  lime.  This  point  will  be  dis- 
cussed more  in  detail  farther  on. 

Sdcnitc  or  Gypsum,  sulfate  of  lime  with  about  14  per  cent 
of  water,  though  not  as  abundant  in  nature  as  the  carbonate  or 
limestone,  is  a  very  widely  disseminated  mineral  and  often 
occurs  in  large  masses  over  considerable  areas.  These  are  un- 
doubtedly in  most  cases  the  result  of  evaporation  of  sea  water 

1  Bull.  No.  i,  U.  S.  Dept.  Agr.  Veg.  Path,  and  Physiol.  Investig. 


THE  MAJOR  SOIL-FORMING  MINERALS.  43 

(see  p.  26),  more  rarely  of  the  transformation  of  limestone. 
In  mass  it  frequently  resembles  the  latter,  but  is  readily  dis- 
tinguished by  its  softness ;  it  does  not  grit  between  the  teeth, 
is  readily  cut  with  a  knife  and  does  not  effervesce  with  acids. 
Very  commonly  it  occurs  in  crystals,  which  are  easily  split  into 
thin  plates.  The  crystals  are  very  frequently  found  imbedded 
in  gray  or  bluish,  tough  clays,  in  rosettes,  or  flat  sheets  which 
mostly  show  characteristic  incurrent  angles  (caused  by  twin- 
ning), and  are  hence  known  as  "  swallowtail  "  crystals.  Such 
sheets  of  selenite  are  popularly  called  "  isinglass,"  which  name 
however  is  equally  applied  to  the  mineral  mica  (see  p.  35). 

Gypsum  is  only  exceptionally  an  abundant  ingredient  of 
soils;  yet  such  soils  prevail  quite  extensively  on  the  upper  Rio 
Grande,  in  New  Mexico  and  adjacent  portions  of  Chihuahua, 
Coahuila,  and  on  the  Staked  Plains  of  Texas.  Here  whole 
ranges  of  hills  are  sometimes  composed  of  gypseous  sand,  bear 
a  scanty,  peculiar  vegetation,  and  are  ill  adapted  to  agricultural 
use.  It  may  be  said  in  general  that  few  naturally  gypseous 
soils  are  very  productive.  This  is  largely  because  of  the  very 
heavy  clays  which  commonly  accompany  it,  as  the  compound  it- 
self is  not  only  not  hostile  to  plant  life  but  is  in  extended  use  as 
a  valuable  fertilizer  ("land  plaster")  for  special  purposes. 
From  causes  not  fully  understood  as  yet,  it  particularly  pro- 
motes the  growth  of  leguminous  plants,  notably  the  clovers; 
and  as  stated  in  chapter  9,  it  also  specially  favors  nitrification  in 
soils.  In  the  arid  region  it  renders  important  service  in  the 
neutralization  of  "  black  alkali  "  or  carbonate  of  soda  in  alkali 
soils.  Being  soluble  in  400  parts  of  water,  it  easily  penetrates 
downward  in  most  soils,  and  in  doing  so  effects  changes  in  the 
zeolitic  portions,  setting  free  potash  from  silicates  and  thus  in- 
directly supplying  plants  with  this  essential  ingredient  in  a 
soluble  form.  About  200  pounds  per  acre  is  an  ordinary  dose. 

For  agricultural  use  the  rock  gypsum  is  ground  in  mills 
so  as  to  be  easily  distributed,  and  dissolved  by  the  soil  water. 
Frequently,  however,  it  occurs  in  the  soft  granular  form 
(gypseous  marl)  requiring1  only  light  crushing;  thus  in  the 
bills  bordering  the  Great  Valley  of  California,  and  in  parts  of 
New  Mexico  and  Texas. 

Iron  Minerals. — In  connection  with  calcite  and  dolomite,  the 


44  SOILS- 

several   minerals  constituting  the  common  iron  ores  require 
mention.     One  of  these  is  : 

Iron  Spar  or  siderite ;  carbonate  of  iron,  corresponds  in  com- 
position to  calcite  and  dolomite  and  crystallizes  in  the  same 
form.  It  sometimes  occurs  in  large  masses  and  is  an  import- 
ant iron  ore,  brownish-white  in  color,  and  when  compact  re- 
sists the  attack  of  atmospheric  oxygen  remarkably  well.  Like 
the  carbonates  of  lime  and  magnesia,  it  is  soluble  in  carbonated 
water,  and  its  deposits  are  undoubtedly  formed  from  such 
solutions.  The  latter  are  copiously  formed  wherever  ferment- 
ing or  decaying  organic  matter  is  in  contact  with  iron-bearing 
materials,  such  as  rust-colored  sands  or  clays;  and  if  the 
solution  so  formed  can  percolate  without  coming  in  contact 
with  air,  iron-spar  is  formed.  But  whenever  the  solution 
comes  in  contact  with  air,  it  absorbs  oxygen  and  the  ferrous 
carbonate  is  converted  into  ferric  hydrate  or  rust,  mineralogi- 
cally  known  as : 

Limonite  or  brown  iron  ore.  This  ore  is  frequently  found 
deposited  on  the  upper  surface  of  clay  layers  traversing  sandy 
strata,  the  clay  having  arrested  the  carbonate  solution  and  thus 
given  time  to  the  air  to  effect  the  change.  Sometimes  such 
deposits  form  great  masses  in  rock-caves,  fissure-veins,  or 
crevices;  and  like  siderite,  it  is  an  important  iron  ore,  though 
frequently  quite  impure,  as  in  the  case  of  bog  ore,  which  is 
formed  in  ill-drained  subsoils.  It  is  also  sometimes  found  as 
the  residue  from  the  weathering  of  rocks  rich  in  hornblende 
or  pyroxene,  and  in  this,  as  well  as  in  other  cases,  is  pulveru- 
lent, constituting  yellow  ochre.  It  makes  a  rust-colored  streak 
on  biscuit  porcelain  or  unglazed  queensware.  //  is  the  coloring 
material  of  all  yellow  or  "  red  "  soils  and  clays,  as  well  as  of 
brown  sandstones,  which  are  cemented  by  it. 

As  is  well  known,  such  clays  and  sandstones  become  dark 
red  by  heating  or  "  burning,"  as  in  the  case  of  common  brick 
clays;  the  brown  or  yellow  ferric  hydrate  losing  its  water  and 
becoming  red  ferric  oxid.  The  latter  sometimes  occurs  in 
nature  in  the  impure,  pulverulent  condition,  constituting  "  red 
ochre";  but  more  commonly  and  abundantly  it  is  found  in  the 
form  of 

Hematite  or  red  iron  ore,  which  is  sometimes  formed  in 


THE  MAJOR  SOIL-FORMING  MINERALS.  45 

nature  by  limonite  losing  its  water,  but  more  commonly  in 
different  ways.  It  is  but  rarely  found  in  soils  and  is  of  no 
special  interest  in  that  connection. 

A  fourth  form  of  iron  ore,  quite  common  in  the  soils  of  some 
regions,  is 

Magnetite  or  magnetic  iron  ore,  also  known  as  lodestone. 
This  mineral,  the  oxygen-compound  of  iron  corresponding  to 
"blacksmith's  scale,"  also  occurs  in  large  masses  and  is  an 
important  and  usually  a  very  pure  iron  ore.  It  occurs  very 
commonly  disseminated  through  certain  rocks,  and  in  their 
weathering  it  remains  unattacked  and  thus  passes  unchanged 
into  the  soils  and  sands,  constituting  the  "  black  sand  "  so  well 
known  to  gold  miners  and  almost  universally  present  in  the 
alluvial  soils  of  the  Pacific  coast.  These  black  grains  are  of 
course  attracted  by  the  magnet  and  can  thus  be  easily  recog- 
nized and  extracted.  In  soils  they  are  simply  inert,  like  quartz 
sand. 

But  while  the  ore  is  of  little  interest  to  the  farmer,  it  is  quite 
otherwise  with  the  compound  of  this  oxid  with  water,  the 
ferroso-ferric  hydrate;  intermediate  in  composition  between 
the  white  ferrous  and  the  brown  ferric  hydrates.  As  men- 
tioned above,  the  black  silicate  minerals,  such  as  hornblende 
and  pyroxene,  are  bottle-green  when  seen  in  thin  sections. 
Nearly  the  same  color,  with  modifications  running  toward  blue 
and  bright  green,  is  often  seen  in  natural  clays  and  rocks, 
and  is  almost  always  caused  by  the  ferroso-ferric  hydrate. 
Such  materials  always  become  red  or  reddish  when  heated  by 
the  formation  of  red  ferric  oxid;  while  when  exposed  to  damp 
air,  they  assume  the  rust  color  of  ferric  hydrate. 

Reduction  of  ferric  hydrate  in  ill-drained  soils. — \Yhen  such 
oxidized,  rust-colored  clays  or  soils  are  exposed  to  the  action 
of  fermenting  organic  matter,  the  first  effect  observed  is  the 
change  of  color  from  rusty  to  bluish  or  greenish,  by  the  reduc- 
tion of  the  ferric  to  ferroso-ferric  hydrate.  Afterward,  if  the 
action  is  continued,  the  solution  of  ferrous  carbonate  ( see 
above)  may  be  formed,  and  the  greenish  or  bluish  color  may 
disappear. 

The  importance  of  this  reaction  to  farming  practice  lies  in 
the  fact  that  the  blue  or  green  tint,  wherever  it  occurs,  indi- 
cates a  lack  of  aeration,  usually  by  the  stagnation  of  water,  in 


46  SOILS. 

consequence  of  imperfect  drainage.  Such  a  condition,  always 
injurious  to  plants,  becomes  doubly  so  when  it  is  associated 
with  the  formation  of  a  metallic  solution,  such  as  ferrous 
carbonate,  and  promptly  results  in  the  languishing  or  death  of 
plants  in  consequence  of  the  poisoning  of  their  roots.  In  the 
presence  of  sulfates  such  as  gypsum,  the  formation  of  iron 
pyrites  (ferric  bisulfid)  and  sulfuretted  hydrogen,  is  likely  to 
take  place.  Moreover,  under  the  same  conditions  the  phos- 
phoric acid  of  the  soil  may  be  concentrated  into  ferrous  or 
ferric  phosphate,  which  pass  into  deposits  of  bog  ore  in  the 
subsoil. 


CHAPTER  IV. 

THE  VARIOUS  ROCKS  AS  SOIL-FORMERS. 

Rock-weathering  in  arid  and  humid  Climates. — From  what 
has  been  said  in  the  preceding  chapters  of  the  physical  and 
chemical  agencies  concerned  in  rock-weathering,  it  is  obvious 
that  climatic  differences  may  materially  influence  the  character 
of  the  soils  formed  from  one  and  the  same  kind  of  rock.  Since 
kaolinization  is  also  a  process  of  hydration,  the  presence  of 
water  must  greatly  influence  its  intensity,  and  especially  the 
subsequent  formation  of  colloidal  clay ;  so  that  rocks  forming 
clay  soils  in  the  region  of  summer  rains  may  in  the  arid  regions 
form  merely  pulverulent  soil  materials.  Many  striking  ex- 
amples of  these  differences  may  be  observed,  c.  g.,  in  comparing 
the  outcome  of  the  weathering  of  granitic  rocks  in  the  southern 
Alleghenies  with  that  of  the  same  rocks  in  the  Rocky  Moun- 
tains and  westward,  especially  in  California  and  Arizona.  The 
sharpness  of  the  ridges  of  the  Sierra  Madre,  and  the  roughness 
of  the  hard  granitic  surfaces,  contrasts  sharply  with  the 
rounded  ranges  formed  by  the  "  rotten  "  granites  of  the  At- 
lantic slope,  where  sound,  unaltered  rock  can  sometimes  not 
be  found  at  a  less  depth  than  forty  feet ;  while  at  the  foot  of 
the  Sierra  Madre  ridges,  thick  beds  of  sharp,  fresh  granitic 
sand,  too  open  and  pervious  to  serve  as  soils,  cover  the  upper 
slopes  and  the  "  washes  "  of  the  streams,  causing  the  latter  to 
sink  out  of  sight.  A  general  discussion  of  the  kinds  of  soils 
formed  from  the  various  rocks  must,  therefore,  take  these 
differences  into  due  consideration. 

GENERAL   CLASSIFICATION    OF    ROCKS. 

Rocks  may  be  broadly  classified  into  three  categories,  viz : 

1.  Sedimentary  rocks,  formed  by  deposition  in  water  and 
hence  more  or  less  distinctly  stratified. 

2.  MctamorpJiic  rocks,  formed  from  rocks  originally  sedi- 
mentary, by  subterranean  heat  in  presence  of  water.     Usually 

47 


48 


SOILS. 


crystalline,  that  is,  composed  of  more  or  less  distinct  (large  or 
minute)  crystals  of  one  or  several  of  the  minerals  mentioned 
above. 

3.  Eruptive  rocks,  ejected  in  the  molten  state  from  vol- 
canoes or  fissures;  crystalline  or  not,  according  to  slow  or 
rapid  cooling. 

Sedimentary  Rocks. — Sedimentary  rocks  are  forming  to-day 
by  deposition  from  either  sea  or  fresh  water,  precisely  as  they 
were  in  the  most  remote  geological  times;  the  oldest  clearly 
sedimentary  rocks  being  sometimes  undistinguishable  in  their 
nature  and  composition  from  the  very  latest  immediately  pre- 
ceding our  present  time.  They  may  for  the  purposes  of  the 
present  work  be  simply  classified  as  follows : 

1.  Limestones,   formed   in   comparatively  shallow   seas,  or 
fresh  water  basins,  from  the  calcareous  shells  or  skeletons  of 
various  organisms. 

2.  Sandstones,  and  conglomerates   (sometimes  called  pud- 
ding-stones) formed  from  the  debris  of  pre-existing  rocks  dis- 
integrated by  the  agencies  described  above,   (chap.   1-2),  re- 
cemented  by  means  of  solutions  of  one  or  several  substances, 
such  as  silex,  carbonate  of  lime,   ferric  hydrate  and  others. 
Loose  sands  and  gravels  are  the  initial  stages  of  such  rock  for- 
mation as  well  as  the  results  of  their  disintegration. 

3.  Clays,  Claystoncs  and  Clay  shales,  consisting  of  clay  sub- 
stance with  more  or  less  sand,  and  soft  or  hard  according  to 
the  nature  of  the  waters  or  solutions  that  may  have  acted  upon 
them,  with  or  without  the  aid  of  heat.     These  rocks  can  only 
be  formed  in  comparatively  quiet  or  "  back  "   waters,   since 
clay  would  not  ordinarily  be  deposited  in  moving  water. 

Mctamorphic  Rocks. — The  effects  of  subterranean  heat  or 
metamorphism  upon  the  sedimentary  rocks  may  be  roughly 
stated  as  follows: 

Limestones  are  transformed  into  marbles  of  various  degrees 
of  purity,  according  to  the  nature  of  the  original  rocks. 

Sandstones  when  cemented  by  silex  are  transformed  into 
quartzite,  of  greater  or  less  purity  according  to  the  nature  of 
the  "  sand  "  entering  into  its  composition.  When  cemented 
by  materials  other  than  quartz,  these  also  will  be  segregated 
in  the  form  of  various  minerals  in  the  body  of  the  rock. 


THE  VARIOUS  ROCKS  AS  SOIL-FORMERS. 


49 


The  clay  rocks  form  the  most  varied  products  under  the  in- 
fluence of  (aqueo-igneous)  metamorphism ;  granites,  gneiss, 
syenite  and  hornblendic  schist  are  among  the  most  common. 
The  great  variations  in  the  composition  of  clayey  materials 
account  for  the  correspondingly  great  variations  in  the  nature 
of  the  resultant  metamorphic  rocks. 

Igneous  or  Eruptive  Rocks. — These  are  usually  divided  into 
two  groups ;  the  one  characterized  by  a  large  proportion  of  free 
quartz  (silicic  acid),  and  hence  designated  as  acidic,  and  usu- 
ally of  a  light  tint;  the  other  the  basic,  containing  little  or  no 
free  quartz,  and  commonly  of  a  dark  tint  caused  by  the  pres- 
ence of  a  large  amount  of  iron  (contained  in  pyroxene,  more 
rarely  in  hornblende). 

Of  the  latter  class  are  the  dark  "  basaltic  "  rocks  constituting  the 
mass  of  the  enormous  eruptive  sheet  of  the  Pacific  Northwest,  covering 
the  greater  part  of  Washington,  Oregon  and  northeastern  California. 
The  lavas  of  the  Hawaiian  islands  are  of  the  same  class  and  even  more 
basic  ;  while  the  eruptives  of  Nevada,  middle  and  southern  California, 
and  eastward  to  the  Rocky  Mountains,  are  mostly  of  the  light-colored, 
acidic  type.  The  same  is  largely  true  of  the  rocks  of  the  Andes  of 
Central  and  South  America,  the  gray  "  Andesites,"  also  represented  in 
the  Caucasus. 

As  one  and  the  same  eruptive  material  may,  according  to 
the  greater  or  less  rapidity  of  cooling,  appear  as  a  glassy  mass 
(obsidian,  pumice,  volcanic  ash,  tuff,  etc..)  or  as  a  crystalline 
rock  resembling  coarse  granite  in  structure,  it  is  not  easy  to 
identify  them  in  all  their  various  forms.  This  can  frequently 
be  done  only  by  ascertaining  their  component  minerals  by  the 
microscope,  or  by  chemical  analysis.  The  same  is  sometimes 
true  of  metamorphic  rocks;  and  as  in  the  latter,  the  several 
feldspars  and  quartz,  with  pyroxene  instead  of  hornblende,  con- 
stitute the  predominant  soil-forming  minerals.  More  rarely, 
garnet,  chrysolite,  leucite  and  other  silicates  require  considera- 
tion. 

Generalities  regarding  the  Soils  derived  from  various  Rocks. 

It  is  hardly  necessary  to  insist  that  as  in  the  case  of  the 
rocks  composed  of  single  minerals,  already  referred  to  above. 
4 


50  SOILS. 

the  predominant  mineral  or  minerals  of  compound  rocks  de- 
termine the  facility  of  weathering,  as  well  as  the  quality  of  the 
soil  resulting  therefrom.  Since  rocks  are  named  essentially 
in  accordance  with  the  kinds  of  minerals  that  constitute  their 
regular  mass,  the  proportion  in  which  the  several  constituents 
stand  to  each  other  may  vary  greatly.  Thus  a  granite  may 
consist,  over  considerable  areas,  mainly  of  a  mixture  of  potash 
feldspar  and  quartz ;  in  others,  mainly  of  quartz  and  mica  with 
little  feldspar.  Very  frequently,  hornblende  replaces  mica  par- 
tially or  wholly.  The  latter  will  weather  much  more  slowly 
than  feldspar  or  hornblende,  and  will  produce  an  inferior  soil 
when  decomposed.  Allowing  for  such  variations,  a  fairly  ap- 
proximate general  estimate  of  the  quality  and  peculiarities  of 
soils  from  crystalline  rocks  may  nevertheless  be  made.  To 
some  extent  such  estimates  must  make  allowance  not  only  for 
the  chief  ingredients,  but  also  for  those  which  are  called  "  ac- 
cessory "  or  characteristic,  and  which  while  not  present  in 
large  amount,  may  nevertheless  exert  a  considerable  influence 
upon  the  quality  of  the  soil. 

Soils  from  granitic  and  crystalline  rocks. — In  the  case  of 
the  (potash-feldspar)  granite  soils  it  is  generally  admissible 
to  expect  that  they  will  be  fairly  supplied  with  phosphoric 
acid,  because  in  the  great  majority  of  cases,  minute  crystals  of 
apatite  (phosphate  of  lime)  are  more  or  less  abundantly  scat- 
tered through  it.  From  the  potash  feldspar  present,  granite 
soils  may  always  be  relied  on  for  a  good  supply  of  potash  for 
plant  use;  on  the  other  hand,  unless  hornblende  be  present, 
they  are  pretty  certain  to  be  deficient  in  lime,  since  neither 
lime,  feldspar  nor  calcite  are  probable  accessory  ingredients 
of  this  rock. 

Granite  is  exceedingly  apt  to  weather  by  mechanical  disin- 
tegration far  in  advance  of  its  chemical  decomposition.  It  is 
therefore  common  to  find  in  sedentary  soils  overlying  granite, 
a  gradual  increase  of  grains  of  its  component  crystalline  min- 
erals as  we  descend  in  the  subsoil ;  until  finally  the  latter  grades 
off  into  rock  almost  unchanged  save  in  lacking  coherence. 
This  is  seen  strikingly  in  the  southern  Appalachians,  as  well  as 
in  the  Sierra  Nevada  and  Sierra  Madre  of  California;  at  Cin- 
tra  in  Portugal,  at  Heidelberg  in  Germany,  and  elsewhere. 

But  of  the  rocks  that  resemble  granite  and  are  popularly  so 


THE  VARIOUS  ROCKS  AS  SOIL-FORMERS.  5  i 

called,  a  good  many  are  not  "  true  to  name  "  and  therefore 
form  soils  differing  materially  from  the  type  just  mentioned. 

Thus  the  so-called  granite  areas  of  the  Sierra  Nevada  of  California 
are  largely  occupied  by  a  rock  containing,  besides  quartz,  chiefly  soda- 
lime  feldspar  and  some  hornblende,  and  scarcely  any  mica.  It  is  more 
properly  a  diorite  (grano-diorite) ;  the  soils  formed  from  it  are  rather 
poor  in  potash,  not  strongly  calcareous,  and  quite  poor  in  phosphoric 
acid.  On  account  of  the  small  proportion  of  hornblende  (unusual  in 
diorites),  these  soils  are  light-colored  (not  "  red  "  ),  and  bear  a  growth 
of  small  pine  instead  of  the  usual  oak  growth  of  the  lower  Sierra 
slopes. 

What  is  said  of  granite  soils  is  also  generally  true  of  those 
formed  from 

Gneiss,  which  is  composed  of  the  same  minerals  as  granite, 
but  has  a  slaty  cleavage  and  on  that  account  when  upturned  on 
edge,  weathers  rather  more  rapidly  than  most  granites. 
Owing  to  the  frequent  occurrence  of  lenticular  masses  of  quartz 
in  gneiss,  its  soils  are  more  commonly  of  a  siliceous  nature 
than  are  those  of  the  true  granite  regions,  and  not  as  "  strong  " 
as  the  latter.  This  is  the  more  true  since  gneiss  often  passes 
gradually  into  mica  schist,  which,  being  a  mixture  of  quartz 
and  mica  only,  not  only  weathers  very  slowly  but  also  supplies 
but  little  of  any  importance  to  plants,  to  the  soils  formed 
from  it.  Such  soils  would  mostly  be  absolutely  barren  but  for 
the  frequent  occurrence  in  the  rock,  of  accessory  minerals  that 
yield  some  substance  to  the  soil.  Yet  it  remains  true  that  in- 
asmuch as  gneiss  and  mica-schists  are  among  the  rocks  in 
which  mineral  veins  most  commonly  occur,  the  proverbial 
barrenness  of  mining  districts  is  very  frequently  traceable  to 
these  rocks.  The  same  may  be  said  of  some  of  the  related 
rocks,  such  as  gabbro,  minette  and  others. 

Normal  diorite  consists  of  hornblende  and  soda-feldspar, 
with  more  or  less  quartz. 

The  soils  derived  from  certain  diorites  of  the  Sierra  Nevada 
of  California  have  just  been  referred  to.  Rut  these  granite- 
like  diorites  are  on  the  whole  exceptional ;  it  should  be  added 
that  the  (diabasic)  "  greenstones  "  of  the  Eastern  United 
States  and  of  the  Old  World,  which  are  usuallv  much  finer- 


52  SOILS. 

grained,  do  not  form  the  mass  of  fine,  angular  debris  consti- 
tuting the  subsoil  in  the  Sierra  Nevada,  but  weather  into 
rounded  masses  and  fine-grained  soils  possessing,  on  the  whole, 
a  fair  fertility,  though  liable  to  contain  an  excessive  proportion 
of  silex  in  various  forms. 

Of  the  eruptive  rocks  as  a  class  it  is  often  said  that  they  form 
very  productive  soils ;  yet,  as  these  rocks  differ  widely  from 
each  other  in  composition,  this  statement  must  be  taken  with  a 
great  deal  of  allowance.  Very  many  of  them  decompose  with 
extreme  slowness  on  account  of  their  glassy  nature ;  this  is  par- 
ticularly true  of  obsidian,  pumice  stone,  and  the  "  volcanic  ash  " 
derived  from  its  pulverization,  and  which  is  found  unchanged, 
in  sharp  scales,  among  the  decayed  minerals  of  other  rocks  in 
complex  soils.  Other  volcanic  ash,  however,  being  formed  by 
the  pulverization  of  crystalline  or  of  basic  lavas,  weathers 
rather  readily,  as  already  stated;  so  that  certain  plants  take 
possession  in  the  course  of  a  few  years.  The  general  classifi- 
cation into  basic  and  acidic  rocks,  given  above,  is  of  importance 
in  connection  with  soil  formation  from  eruptive  masses;  for 
the  basic  rocks  are  much  more  easily  attacked  by  the  atmos- 
pheric agencies  than  the  acidic  class. 

A  broad  distinction  must,  however,  be  made  between  the  basic  rocks 
of  the  basaltic  class,  which  contain  black  pyroxene  as  a  prominent 
ingredient,  and  those  which,  like  many  trachytes,  are  rich  in  feldspathic 
minerals.  The  latter  are  naturally  rich  in  alkalies  (potash  and  soda) 
which  they  impart  to  the  corresponding  light-colored  soils ;  while  the 
black  basaltic  rocks  and  lavas  weather  into  "red"  soils,  sometimes 
containing  extraordinary  amounts  of  iron  (ferric  hydrate)  and  (from  the 
lime-feldspars  they  contain)  a  fair  supply  of  lime,  but  oftentimes  very 
little  potash.  Experience  seems  to  prove  that  the  red  basalt  soils  are 
mostly  rather  rich  in  phosphoric  acid ;  this  is  especially  true  of  the 
country  covered  by  the  great  eruptive  sheet  of  the  Pacific  Northwest, 
in  the  rocks  of  which  the  microscope  readily  detects  the  presence  of 
numerous  needles  of  apatite  (lime  phosphate).  The  same  is  true  of 
the  highly  iron-bearing  soils  from  the  black  basaltic  lavas  of  the  Hawaiian 
islands,  even  though  they  have  been  leached  of  all  but  traces  of  lime 
and  potash.  All  these  soils  are  physically  "  light "  and  easily  workable, 
since  the  rocks  in  question  contain  but  little  alumina  from  which  to 
form  clay  ;  they  are  sometimes  extremely  rich  in  iron,  even  to  the 
extent  of  being  capable  of  serving  as  iron  ores. 


THE  VARIOUS  ROCKS  AS  SOIL-FORMERS.  53 

The  soils  derived  from  trachytes  and  trachytic  lavas  are 
generally  light-colored  and  light  in  texture;  the  latter  from 
the  presence  of  a  large  proportion  of  volcanic  glass,  together 
with  undecomposed  crystalline  minerals.  These  are  usually 
rich  in  potash,  but  poor  in  lime  and  phosphates.  The  high 
quality  of  the  wines  of  the  lower  Rhine  has  been  ascribed  to 
these  soils,  which  however  vary  greatly  within  the  areal  limits 
of  the  production  of  the  high-grade  wines,  not  only  from  gray 
trachytes  to  dark  colored,  highly  augitic  basalt,  but  also  to 
acidic  quartz  porphyries  or  rhyolites,  and  clay-slates. 

The  rhyolites  on  the  whole  yield  the  poorest  soils  among  the 
eruptive  rocks;  they  are  slow  to  weather  at  best,  and  the  soils 
produced  are  poor  and  unsubstantial,  largely  from  the  predom- 
inance of  quartz  and  undecomposable,  glassy  material ;  of  which 
the  phonolites  are  the  extreme  type,  resisting  the  influence  of 
the  atmospheric  agencies  just  as  would  so  much  artificial  glass. 
Soils  consisting  largely  of  volcanic  glass  may  be  found  cover- 
ing considerable  areas  in  the  Sierra  Nevada  of  California. 
Such  "  volcanic  ash  "  soils  are  usually  very  unthrifty,  and  bear 
a  growth  of  small  pines. 

Soils  from  sedimentary  rocks. — Limestones,  when  pure  and 
hard,  are  very  slow  to  disintegrate,  and  are  also  very  slowly 
attacked  by  carbonated  water  (see  chap.  3.  page  41).  Soft 
impure  and  vesicular  limestones  are,  however,  very  rapidly  at- 
tacked, especially  when  underlying  a  surface  clothed  with  the 
luxuriant  vegetation  that  usually  flourishes  on  soils  rich  in 
lime.  The  popular  adage  that  "  a  limestone  country  is  a  rich 
country,"  is  of  almost  universal  application  and  stamps  lime, 
from  the  purely  practical  standpoint,  as  one  of  the  most  im- 
portant soil  ingredients. 

Residual  Limestone  Soils. — Striking  examples  of  the  forma- 
tion of  large,  fertile  soil  areas  by  the  leaching  out  of  limestones 
are  found  in  the  States  of  Alabama,  Mississippi,  Louisiana  and 
Texas,  where  the  fertile  black  prairies  have  been  largely  thus 
formed.  The  ''  blue-grass  "  country  of  Central  Kentucky  is 
another  case  in  point. 

The  following  table  shows  a  representative  example  of  the 
relative  composition  of  the  (cretaceous)  ''  Rotten  Limestone'' 
of  Mississippi,  and  the  "  residual  "  soil-stratum  derived  from 
it.  The  average  thickness  of  the  layer  of  residual  clay  above 


54 


SOILS. 


the  limestone  is  about  eight  feet,  but  ranges  from  seven  to  ten ; 
the  upper  layers  of  the  limestone  are  somewhat  softened,  but 
the  rock  is  always  fresh  at  twelve  feet,  from  which  depth  the 
sample  analyzed  was  taken,  in  a  cistern  adjoining  the  field  from 
which  the  soil  and  subsoil  were  procured.  The  black  soil 
varies  in  depth  from  8  to  15  inches;  then  there  is  a  change  to 
a  brownish  subsoil,  reaching  down  to  about  two  feet,  and  in 
drying  cleaving  into  prismatic  fragments.  The  black  soil  has 
here  in  the  highest  degree  the  peculiarity  of  crumbling  in  dry- 
ing from  its  water-soaked  condition,  so  that  it  may  be  plowed 
when  wet  without  injury,  although  in  the  roads  it  works  up 
into  the  toughest  kind  of  mud.  The  prairie  is  sparsely  tim- 
bered with  compact,  fair-sized  black-jack  oak,  accompanied 
originally  by  red  cedar. 

The  limestone  derives  its  popular  name  of  "  rotten  "  from 
its  being  usually  soft  enough  to  be  cut  with  a  knife  or  hatchet, 
and  is  therefore  somewhat  used  for  building,  and  for  burning 
lime. 

COMPOSITION  OF  LIMESTONE,  AND  RESIDUAL  SOIL  AND  SUB-SOIL,  FROM  BLACK 
PRAIRIE,  MONROE  CO.,  MISSISSIPPI. 


"  ROTTEN 

LIMESTONE." 

SUBSOIL 
(YELLOW). 

SOIL 
(BLACK). 

FINE  EARTH. 
Chemical  analysis  of  fine  earth. 

Depth..  1  2  ft. 

2-3  ft. 

15  ins. 

Insoluble   matter  

10  90 

71  CA 

78.20 

Soluble  silica  

Potash  (K,O)  

2C 

CA 

•?•» 

Soda  (Na,O)  

72 

23 

08 

Lime  (CaO)  

A  C  7O 

I  O8 

i  11 

Magnesia  (MgO)  

88 

.77 

-,6 

Br.  Ox.,  of  Manganese  (Mn3O4)  

oc 

i  j. 

Peroxide  of  Iron   (FeO)  

I  A2 

C  42 

Alumina   (A1,,O,)  

I  96 

11  I  Z. 

14.22 

Phosphoric  Acid  (PaO5)  

.OC 

IO 

Sulfuric  Acid  (SO3)  

O7 

Carbonic   Acid  (CO,)  

7C  77 

Waterand   Organic   matter  

JWJ 

2  84 

(t  OO 

Total  

0086 

Humus  

I  O7 

"       Ash  

d  78 

Hygroscopic  moisture  

IO  If. 

i-'.S- 

absorbed  at  °C  

10° 

IQ° 

THE  VARIOUS  ROCKS  AS  SOIL-FORMERS.  55 

It  appears  from  the  above  table  that  in  the  change  from  the 
original  limestone  to  the  soil  mass  as  found  at  three  feet  depth, 
81.5%  of  the  lime  carbonate  has  been  eliminated  by  leaching, 
leaving  behind  somewhat  less  than  one  fifth  of  the  original 
mass.  Taking  the  average  depth  of  the  soil  mass  at  8  feet, 
this  thickness  of  material  has  required  about  45  feet  of  the 
rotten  limestone.  Considering  that  notwithstanding  the  ten- 
acity of  the  clay  soil,  some  of  it  must  in  the  course  of  time 
have  been  washed  away,  we  may  safely  assume  that  the  orig- 
inal rock  surface  was  from  50  to  60  feet  higher  than  at 
present. 

Sandstone  Soils. — The  indefiniteness  of  the  nature  of  "  sand- 
stones "  as  such  renders  generalizations  in  regard  to  the  soils 
formed  from  them  rather  difficult,  save  as  to  their  physical 
qualities,  which  in  the  nature  of  the  case  are  always  "  light." 
In  the  Old  World  and  in  the  humid  region  generally,  sandstone 
and  sandy  soils  are  usually  spoken  of  as  being  poor,  because 
there  the  sand  almost  always  consists  of  quartz  grains  only,  and 
hence  the  fine  portions  alone  can  be  looked  to  for  plant  nutri- 
tion. Consequently,  the  more  sand  is  seen  in  a  soil,  the  poorer 
it  is  usually  presumed  to  be.  But  this  presumption  would  be 
wholly  erroneous  in  the  arid  regions.  (See  chapt.  6,  p.  86). 

Clearly,  the  nature  of  the  soils  produced  by  the  weathering 
of  sandstones  depends  upon  two  points :  first,  the  nature  of  the 
cement  binding  the  sand  grains,  and  second  the  character  of 
the  latter  themselves. 

Varieties  of  Sandstones. — As  has  been  stated  above,  the 
cements  may  be  roughly  classified  into  five  kinds,  and  their 
intermixtures,  to  wit:  qnartzose  or  siliceous,,  calcareous,  fer- 
ruginous, aluminous  or  clayey,  and  ccolitic.  As  regards  the 
first,  it  is  obvious  that  siliceous  sandstones  will  disintegrate 
with  great  difficulty,  since  neither  the  cement  nor  the  grains 
are  susceptible  of  material  change  by  weathering.  Such  sand- 
stones frequently  pass  insensibly  into  quartz  rock,  and  the 
light,  unsubstantial  soils  they  produce  are  of  the  poorest,  con- 
taining often  mere  traces  of  the  plant-food  ingredients.  This 
of  course,  is  true,  not  only  of  the  soils  formed  by  the  actual 
weathering  of  sandstones,  but  equally  of  those  consisting  of 
quartz-sand  deposited  by  water  or  drifted  by  winds. 


56  SOILS. 

Of  this  character  are  the  pine-forest  soils  of  the  coast  region  of  the 
Gulf  of  Mexico,  particularly  the  "  Sand  hammocks  "  of  the  immediate 
Gulf  border,  from  Mississippi  Sound  to  Charlotte  Harbor,  Florida ;  the 
sandy  lands  of  the  Grand  Traverse  region  of  Michigan,  and  many  other 
minor  areas  in  the  United  States,  usually  characterized  by  a  pine  growth, 
often  more  or  less  stunted,  according  to  the  nature  of  the  sand  grains. 

Calcareous  sandstones  usually  form  a  very  much  better 
class  of  soils,  partly  for  the  intrinsic  reason  given  above  as 
regards  limestones  as  soil-formers.  The  calcareous  cement  is 
very  rarely  pure  calcite;  in  most  cases  it  is  very  impure,  as, 
most  commonly,  is  also  the  "  sand  "  itself.  This  is  explained 
from  the  fact  that  such  rocks  (mostly  soft  and  often  quite  un- 
consolidated)  are,  like  limestones  themselves,  the  result  of  de- 
position in  shallow  seas  or  lakes,  receiving  deposits  from  the 
land  drainage,  and  enriched  by  the  animal  and  vegetable  life 
of  such  waters.  Not  uncommonly  they  contain,  disseminated 
through  them,  grains  of  the  mineral  glauconite  (a  hydrous 
silicate  of  iron  and  potash),  which  readily  supplies  available 
potash ;  while  the  remnants  of  animals  and  plants  furnish 
more  or  less  of  available  phosphates.  Thus  the  general  pre- 
sumption regarding  calcareous  sandstones  is  that  the  derived 
soils  are  of  good  quality,  frequently  of  the  very  best.  The 
same,  however,  does  not  appear  to  be  true  of  sandstones  cem- 
ented by  dolomite;  the  soils  derived  from  magnesian  sand- 
stones are  in  many  cases  noted  for  their  unproductiveness. 
(See  chapt.  3,  p.  42). 

Ferruginous  Sandstones  manifestly  derive  no  important  soil 
ingredients  from  their  cement  when  the  latter  is  measurably 
pure  ferric  hydrate;  and  when  in  addition  the  sand  itself  is 
purely  siliceous,  the  soils  resulting  from  the  disintegration  of 
the  rocks  are  very  poor. 

Such  are,  e.g.,  the  soils  derived  from  the  ferruginous  sandstones  of  the 
Lafayette  formation  in  a  part  of  northern  Mississippi  and  adjacent  por- 
tions of  Tennessee  and  Alabama,  characterized  by  small  scrubby  oak  or 
dwarfed  pine.  On  the  whole,  however,  such  purely  ferruginous  quartz 
sandstones  are  exceptional,  and  should  not  detract  from  the  favorable 
inferences  usually  to  be  drawn  from  the  iron- rust  tint  of  soils  (see 
chapter.  15 


THE  VARIOUS  ROCKS  AS  SOIL-FORMERS. 


57 


Sandstones  with  purely  zcolitic  cement  are  on  the  whole  not 
of  frequent  occurrence,  the  zeolites  forming,  more  commonly, 
the  hard  portion  of  a  clay-sandstone  cement,  which  disinte- 
grates by  their  weathering-out. 

In  regions  where  the  tufaceous  rocks  of  eruptives  prevail,  we  not 
uncommonly  find  the  "  volcanic  ash  "  solidly  cemented  by  a  zeolitic 
mass,  which  is  then  usually  apparent  in  cavities  or  crevices  in  the  form 
of  crusts  or  crystals.  Such  tuffs  are  commonly  rich  in  alkalies  and 
lime,  but  mostly  poor  in  phosphates,  and  in  disintegration  form  soils  of 
a  corresponding  nature.  They  are  largely  represented  in  the  valleys 
off  Puget  Sound,  as  well  as  in  portions  of  central  Montana,  and  north- 
ward. 

Clay-Sandstones  (argillaceous  sandstones)  when  soft,  as  is 
mostly  the  case,  form  as  a  rule  desirable  loam  soils,  of  a  gener- 
alized composition,  difficult  to  predict.  It  is  here  that  the  com- 
position of  the  sand  grains  themselves  most  frequently  comes 
into  play  in  modifying  the  soil  quality.  From  clay-sandstones 
to  claystones  of  various  degrees  of  sandiness  there  is,  of  course, 
every  grade  of  transition,  the  soils  ranging  correspondingly 
in  the  scale  of  lightness  or  clayeyness.  As  a  general  rule,  the 
potash  contents  of  such  soils  are  sensibly  proportioned  to  the 
clayey  ingredient,  at  least  in  the  humid  regions. 

Claystones  (i.  e.,  clays  hardened  by  some  one  or  more  of 
the  cements  mentioned  in  connection  with  sandstones),  will 
in  the  nature  of  the  case,  when  disintegrated  from  the  condi- 
tion in  which  they  lie  in  the  geological  formations,  make  cor- 
respondingly clayey,  heavy  soils,  which  as  experience  shows 
are  usually  rich  in  the  ingredients  of  plant  food,  but  frequently 
too  heavy  and  intractable  in  tillage  to  be  readily  utilized. 

There  are,  of  course,  exceptions  ;  such  as  soils  formed  from  pipe- 
clays, in  which  little  if  any  mineral  plant-food  remains,  and  which  are 
best  used  for  other  purposes  than  agriculture,  unless  under  special  con- 
ditions it  may  be  worth  while  to  reclaim  them  by  fertilization. 

Natural  Clays. — Clays  occur  in  nature  in  a  great  variety  of 
modifications  that  have  received  designations  known  in  com- 
mon life.  Such  are  porcelain  clay,  pipe-clay,  fire-clay,  potters' 


58  SOILS. 

clay,  brick-clay,  and  many  others  of  more  or  less  local  use 
only.  As  these  materials  practically  concern  the  farmer  in 
very  many  cases,  they  may  properly  find  a  brief  discussion 
here. 

The  variety-names  enumerated  above  in  the  order  of  the 
actual  contents  of  the  materials  in  true  clay  substance  ("col- 
loidal clay  "),  are  partly  based  upon  that  fact,  partly  upon  the 
degree  of  plasticity  attained  by  that  substance,  and  essentially 
upon  the  nature  and  amount  of  foreign  admixtures  associated 
with  it.  Thus,  porcelain  clay  is  chalky  kaolinite,  sometimes 
associated  with  enough  of  pure  white  plastic  clay  to  render  it 
workable  in  the  potter's  lathe,  but  more  commonly  requiring 
to  be  molded  in  porous  molds;  it  is  very  refractory  to  heat. 
Pipe-clay  is  also  white,  but  more  plastic  and  usually  less  re- 
factory.  Fire-clay  is  a  refractory  pipe-clay  commingled  with 
some  coarse  infusible  material,  such  as  quartz  sand  (or  the 
same  clay  burnt  and  crushed),  in  order  to  prevent  excessive 
contraction  and  change  of  shape  in  drying  and  burning.  Pot- 
ters' clay  is  a  much  less  pure,  and  from  that  cause  more  fusible 
clay,  which  when  burnt  forms  at  a  moderate  heat  a  semi-fused, 
more  or  less  hard  mass,  such  as  crockery  and  pottery  ware. 
Brick-clay  is  a  still  more  impure  clay,  or  loam,  containing  con- 
siderable sand  and  usually  iron  oxid,  and  largely  falls  already 
within  the  limits  of  tillable  soils  or  subsoils,  rendered  fusible 
by  the  presence  of  relatively  considerable  amounts  of  iron, 
magnesia  and  lime. 

Iron  colors  natural  clays  either  red,  yellow,  green  or  blue ;  the  latter 
two  colors  turning  to  yellow  or  red  on  exposure  to  the  air,  and  to  red 
on  burning.  Black  color  is  usually  due  to  carbon,  such  clays  often 
turning  white  on  heating. 

Clays  containing  much  lime  are  usually  of  a  gray  or  whitish  tint,  and 
like  the  soft  crumbly  limestones  are  often  called  marls,  and  are  used  as 
such  for  land  improvement.  But  it  should  be  understood  that  the 
colors  of  clays,  mostly  derived  from  some  iron  compound,  have  little  to 
do  with  their  uses  in  the  arts,  except  that  no  deeply  colored  clay  (black 
excepted)  is  refractory  in  the  fire. 


THE  VARIOUS  ROCKS  AS  SOIL-FORMERS. 


59 


"  Colloidal "  Clay.1 

In  connection  with  soils,  clay  may  be  defined,  in  the  most 
general  terms,  as  being  the  substance  which  imparts  plasticity 
and  adhesiveness  to  soils  when  wetted  and  kneaded,  and 
which,  when  heated  to  redness,  loses  this  property  completely 
and  permanently,  becoming  hard  and  coherent  in  proportion 
to  the  degree  of  heat  to  which  it  is  exposed. 

In  common  life,  however,  the  name  is  applied  to  the  whole 
of  any  naturally  occurring  earth  which  on  wetting  and  knead- 
ing assumes  a  reasonable  degree  of  plasticity  and  adhesiveness. 
When  the  latter  property  becomes  nearly  or  quite  insensible, 
the  earth  is  designated  as  a  "  loam,"  more  or  less  "  clayey  " 
according  to  the  amount  of  the  pure,  plastic  and  adhesive  ma- 
terial associated  with  the  mineral  powders  and  sand  that  form 
the  bulk  of  most  soils. 

Chemically,  the  pure  clay  substance2  probably  consists  (as 
has  been  stated  above)  of  silica  and  alumina  in  the  proportion 
of  nearly  46  to  40,  the  rest  (14%)  being  water  of  hydration, 
which  is  lost  on  burning  the  clayey  material.  But  while  it  is 
true  that  such  is  the  composition  of  the  plastic  substance  of 
clays,  plasticity  and  adhesiveness  are  by  no  means  invariable 
properties  of  this  compound.  In  its  purest  state,  as  kaolinite, 
it  is  readily  mistaken  for  chalk,  ( and  is  sometimes  used  as 
such),  being  powdery  to  the  touch  and  entirely  devoid  of  plas- 
ticity 3  when  wetted  and  kneaded.  The  microscope  shows  this 

1  This  term  was  first    employed    by  Th.  Schloesing,  in  communications    to    the 
French  Academy  of  Sciences,  and  reported  in  the  Comptes  Kendus  of  that  body  ; 
first  in    1870.     Unaware    of    Schloesing's  work,  the  writer  began  a  full  investiga- 
tion of  the  subject  of  mechanical  soil  analysis  in   1871,  and  published  the  results 
in  iSjj  (Am.  Jour.  Sci.,  Oct.  1873).     Up  to  that  time  the  limited  resources  of  the 
library  of  the  University  of  Mississippi  had  not  given  him  an  opportunity  to  see 
Schloesing's   publication.     The  two  independent  investigations,  chough  conducted 
on  somewhat  different  lines,  gave    of  course  practically  the  same  results,  and  com- 
plement each  other. 

2  There  is  still  some  discussion  as  to  the  chemical  identity  of  colloidal  clay  with 
Kaolinite;  but  the  objections  are  not  convincing. 

1  It  has  of  late  been  attempted  to  extend  the  meaning  of  this  word  to  the  be- 
havior of  all  powders  when  wetted  with  water.  Hut  the  adhesive  plasticity  of 
clay  stands  almost  alone,  in  that  (aside  from  contraction)  it  preserves  in  drying 
the  form  into  which  it  may  have  l>een  molded  while  wet,  even  when  struck^ 
whereas  other  powdery  substances  similarly  treated  at  once  collapse  back  into  the 
original  powder.  The  exclusive  use  of  clay  in  modeling  offers  the  typical  example 
of  plasticity  as  generally  understood.  The  addition  of  any  powdery  substance, 
however  fine,  diminishes  the  plasticity  ot  clay. 


60  SOILS. 

chalky  kaolinite  to  consist  of  minute,  mostly  rounded,  origin- 
ally six-sided,  thin  plates,  which  when  pure  resemble  to  the 
touch  powdered  talc  (soapstone)  or  even  black-lead,  rather 
than  any  clay  known  to  common  life.  But  being  exceedingly 
soft,  the  kaolinite  substance  is  easily  ground  or  triturated  into 
an  extremely  fine  powder ;  and  Johnson  and  Blake  1  succeeded 
in  producing  sensible  plasticity  and  adhesiveness  by  long-con- 
tinued trituration  of  kaolinite  with  water  in  a  mortar.  A 
similar  process,  but  continued  much  longer  by  the  mechanical 
agencies  concerned  in  soil-formation  (see  chapt.  i),  is  un- 
questionably the  chief  factor  concerned  in  the  formation  of 
natural  plastic  clays;  but  whether  this  is  the  only  process  by 
which  the  powdery  kaolinite  may  be  transformed  into  plastic 
clay,  is  a  question  not  definitely  settled.  It  is  at  least  possible 
that  repeated  freezing  and  thawing,  as  well  as  the  action  of 
hot  water,  may  take  a  part  in  the  transformation,  beyond  that 
by  which  they  destroy  the  crumbly  (flocculated)  structure  of 
soils  and  clays,  and  render  them  plastic ;  as  is  done  in  the  ma- 
turing of  clays  by  potters. 

Causes  of  Plasticity. — In  any  case  the  property  of  plasticity 
and  adhesiveness  is  restricted  to  the  particles  so  fine  that  they 
fail  to  settle,  in  the  course  of  24  hours,  through  a  column  of 
pure  water  eight  inches  (200  m)  high,  while  some  are  so  ex- 
tremely minute  that  they  will  not  settle  for  many  months,  and 
even  for  several  years.2  Such  turbid  "  clay  water "  may 

1  American  Journal  of  Science,  2d  Ser.,  Vol.  43,  p.  357. 

2  Williams  (Forsch.  Agr.   Phys.    Vol.  18,  p.  225  ff.)  claims  that   the  diameter  of 
the  minutest  clay  particles  is  one-thousandth  of  a  millimeter,  their  form  being  that 
of  scales  showing  continual  (Brownian)  motion   in   water.     He  maintains  that  the 
plasticity  of  clay  is  due  to  this    minute  size,  and  this  view  has  gained  wide  accept- 
ance in  late  works  on  the  subject.     But  this  assumption  cannot  be  maintained  in 
the  face  of  the  fact  that  nothing  like  the  adhesive  plasticity  of  clay  can  be  attained 
even  by  the  finest   powders   of  other  substances,  least  of  all  by  those   having  the 
closest  mineralogical  resemblance  to   kaolinite,  such  as  graphite  and  talc.     Above 
all,  the  most  persistent  trituration  with    water  utterly  falls  to  restore  plasticity  to 
clay  once  baked  so  as  to  expel  its  water  of  hydration,  although   the  fineness  of  the 
particles  is  thereby  not  only  not  diminished,  but  actually  increased,  by  contraction 
in  heating.     No  powders  however  fine  can  replace  the  functions   of  clay  in   soils, 
viz.  the  maintenance  of  floccules,  and    tilth    dependent   thereupon  ;  and    they  dis- 
tinctly impair  the  plasticity  of  clay.     The   fine  "  slickens  "  of   quartz    mills  merely 
render  soils  containing   them   more  close  and    impervious,  and    more   difficult   to 
flocculate.     Even  gelatinous  masses  like  hydrated  ferric  and  aluminic  oxids  fail  to 
replace  clay  in  its  adhesive  functions. 


THE  VARIOUS  ROCKS  AS  SOIL-FORMERS.  6l 

sometimes  be  found  existing  in  nature,  in  moist,  secluded 
places,  for  weeks  after  the  subsidence  of  the  overflows  of 
rivers  whose  water  is  exceptionally  free  from  dissolved  mineral 
matter. 

Separation  of  Colloidal  Clay, — This  property  of  the  plastic  clay 
substance,  of  diffusing  in  pure  water,  furnishes  the  means  of  separating 
from  it  the  coarser,  sandy  and  silty  portions  of  soils  and  natural  clays, 
and  observing  its  characteristic  properties,  so  far  as  the  almost  un- 
avoidable admixture  of  some  other  substances,  presently  to  be  considered, 
permits. 

In  natural  soils  the  clay  particles  usually  incrust  the  powdery  ingredi- 
ents, cementing  them  together ;  or  themselves  form  complex  aggregates 
(floccules)  of  large  numbers  of  individual  particles.  These  may  be 
loosened  from  their  adhesion  or  cohesion  either  by  prolonged,  gentle 
kneading  of  the  wet  clay,  or  by  more  or  less  prolonged  Digestion  (soak- 
ing) in  hot  water,  or  more  expeditiously,  by  lively  boiling  with  water. 
The  boiling  should  not,  however,  be  prolonged  beyond  the  time  actually 
required  for  disintegration,  since  (as  Osborne  '  has  shown)  long-pro- 
tracted boiling  tends  to  render  the  clay  permanently  less  diffusible. 

From  the  turbid  clay-water  the  diffused  clay  may  be  obtained  either 
by  evaporating  the  water  (which  as  the  bulk  is  very  large,  is  usually 
inconvenient),  or,  more  conveniently,  by  throwing  it  down  from  its 
suspension  by  the  action  of  certain  substances  which  possess  the  prop, 
erty  of  curdling  (coagulating)  the  clay  substance  into  flocculent  masses 
that  settle  quickly.  Of  all  known  substances,  lime,  in  the  form  of 
lime-water,  acts  most  energetically  in  producing  this  change  ;  but  other 
solutions  of  lime,  as  well  as  most  salts  and  mineral  acids,  produce  the 
same  effects  when  used  in  sufficient  quantity.  Common  salt  is  among 
the  most  convenient,  because  it  can  most  readily  be  leached  out  of  the 
clay  precipitate  thus  thrown  down.  This  when  white,  resembles  boiled 
starch,  but  being  usually  colored  by  iron  might  be  easily  mistaken  for 
the  mixed  precipitate  of  ferric  hydrate  and  alumina  so  commonly 
obtained  by  chemists  in  soil  analysis.  When  separated  from  the  water 
and  dried,  the  jelly-like  substance  (  "  colloidal  clay  " )  shrinks  as 
extravagantly  as  would  so  much  boiled  starch,  into  hard,  shiny  crusts  or 
flakes,  which  when  struck  in  mass  are  sometimes  even  resonant,  and 
bear  more  resemblance  to  glue  than  to  the  clay  of  everyday  life.  Like 
glue,  too,  but  much  more  quickly  and  tenaciously,  the  dried  colloidal 

1  Rep.  Conn.  Agr.  Expt.  Sin.,  iSS6,  1887. 


62  SOILS. 

clay  adheres  to  the  tongue,  so  as  to  render  the  separation  painful ;  when 
wetted  it  quickly  bulges  with  great  energy,  and  in  a  short  time  resumes 
its  former  jelly-like  condition.  When  moistened  with  less  water  it 
assumes  a  highly  plastic  and  adhesive  condition,  so  that  it  is  difficult  to 
handle  and  almost  as  sure  to  soil  the  operator's  hands  as  so  much 
pitch. 

Effects  of  Alkali  Carbonates  upon  Clay. — The  carbonate  of 
potash  and  soda,  when  in  very  dilute  solution  (.01  to  .05%) 
exert  upon  diffused  clay  an  effect  the  reverse  of  the  acids  and 
neutral  salts.  They  destroy  the  flocculent  aggregates  formed 
by  precipitation  with  these,  or  naturally  existing  in  the  soil, 
and  tend  to  puddle  the  clay  so  as  to  render  it  impervious  to 
water.  It  is  thus  that  in  the  alkali  lands  of  the  arid  regions 
we  often  find  the  soil  or  subsoil  consolidated  into  a  very  re- 
fractory "  hardpan,"  difficult  to  break  even  with  a  sledge  ham- 
mer and  impossible  to  reduce  to  tilth  until  the  alkali  carbonate 
is  destroyed  by  means  of  a  lime  salt,  such  as  gypsum.  (See 
chapt.  23).  Ammonia  water  also  helps  to  cause  the  diffu- 
sion of  clay  in  water,  but  its  effect  of  course  disappears  upon 
drying.  It  is  probable  that  this  property  of  sodic  carbonate 
can  be  utilized  in  rendering  earth  dams  firmer  and  more  secure 
against  the  penetration  of  water. 


CHAPTER  V. 

THE  MINOR  MINERAL  INGREDIMENTS  OF  SOILS;  MINERAL 
FERTILIZERS  ;  MINERALS  INJURIOUS  TO  AGRICULTURE. 

(A.)     MINERALS    USED   AS    FERTILIZERS. 

OF  minerals  important  in  soil-formation,  not  usually  present 
in  large  amounts  in  rocks,  but  extensively  used  in  fertilization, 
the  following  require  mention: 

Apatite;  phosphate  of  lime  containing  more  or  less  of  the 
chlorids  and  fluorids  of  the  same  metal ;  the  mineral  from 
which  the  phosphoric  acid  of  the  soil  is  mostly  derived.  In 
the  crystallized  condition  when  perfectly  pure  it  is  colorless ; 
but  it  is  mostly  of  a  greenish  tint  (hence  "  asparagus  stone  "). 
The  pure  crystalline  mineral  rarely  occurs  in  large  masses  (as 
in  Canada)  ;  but  small  to  minute  crystals  are  found  widely  dis- 
seminated in  many  rocks  (granites,  "  basalts  "  of  the  Pacific 
Northwest),  thus  passing  into  the  soils  formed  from  these 
rocks.  These  crystals  are  readily  recognized,  being  regular 
six-sided  prisms  with  a  flat  or  obtusely  pyramidal  termination 
(distinction  from  quartz),  and  do  not  effervesce  with  acids 
(distinction  from  calcite).  By  far  the  largest  deposits  of 
this  mineral  occur  in  connection  with  carbonate  of  lime,  in  the 
rock  materials  known  as  phosphorites.  Lime  phosphate  be- 
ing, like  the  carbonate,  soluble  in  carbonated  water,  the  two 
naturally  frequently  pass  into  solution,  and  are  subsequently 
deposited  together.  Most  limestones  contain  a  small  propor- 
tion of  lime  phosphate,  being,  as  already  stated,  formed  from 
the  shells  and  the  framework  of  animal  organisms  usually 
containing  also  phosphates.  But  the  content  of  phosphates 
in  limestones  is  not  readily  apparent  to  the  eye,  and  the  richest 
deposits,  save  such  as  contain  animal  bones,  have  long 
passed  unsuspected  as  to  their  being  anything  else  but  lime- 
stone. Systematic  search  has  now  revealed  the  presence  of 
phosphate  rock  in  numerous  localities,  chiefly  where  limestone 

63 


64  SOILS- 

formations  occur.  In  the  United  States,  in  South  Carolina, 
Florida,  Alabama,  Tennessee,  Kentucky,  Nevada;  in  South 
America,  on  Curagoa  island,  Venezuela ;  in  the  Antilles  on  Som- 
brero, St.  Martins  and  Navassa  islands.  In  Africa,  in  Algiers 
and  Tunisia;  in  Europe,  in  Spain  (Estremadura,  one  of  the 
first  deposits  known),  France,  Belgium  and  the  adjacent  parts 
of  Germany;  in  Bohemia  and  Galicia  in  Austria;  and  very  ex- 
tendedly  in  European  Russia.  Many  islands  of  Oceanica  sup- 
ply phosphorites  derived  from  the  decomposition  of  bird  guano 
by  the  coral  limestone. 

Unfortunately  the  percentage  of  phosphate  in  a  large  proportion  of 
these  materials  is  not  sufficiently  high  to  make  their  conversion  into 
water-soluble  superphosphate  economically  possible  at  the  present  time  ; 
since  all  the  calcic  carbonate  present  must  also  be  converted  into  com- 
paratively worthless  sulphate  (gypsum )  by  the  use  of  sulfuric  acid ; 
and  as  yet  no  practicable  method  for  avoiding  this  difficulty  has  been 
found. 

"  Thomas  Slag." — Probably  the  nearest  approach  to  such  a  method 
is  indicated  by  the  fact  that  a  compound  containing  four  instead  of 
three  molecules  of  lime  to  one  of  P2O5,  such  as  is  contained  in  the 
"  Thomas  slag  "  of  the  basic  process  of  steel  manufacture,  is  nearly  or 
in  some  cases  ("sour"  soils)  quite  as  effective  for  the  nutrition  of 
plants  as  the  water-soluble  superphosphate.  This  discovery  has  rendered 
available  for  agricultural  use  the  phosphoric  acid  contained  in  the 
enormous  deposits  of  limonite  iron  ore  known  as  bog  ore,  which  con- 
tains a  large  proportion  of  ferric  phosphate  and  from  that  cause  has 
until  lately  been  excluded  from  the  manufacture  of  wrought  iron  and 
steel.  It  is  reasonable  to  hope  that  by  some  analogous  process  the 
low-grade  phosphorites,  such  as  those  of  Nevada  and  the  plains  of 
Russia,  will  also  in  the  course  of  time  become  available  for  agricultural 
use.  Extremely  fine  grinding  and  washing  (producing  "  floats  "  )  has 
been  resorted  to  for  the  purpose  of  rendering  the  raw  phosphorites 
effective  in  fertilization.  But  while  this  is  successful  on  some  soils,  on 
others  the  "  floats"  remain  almost  inert ;  so  that  this  method  has  found 
only  limited  acceptance. 

Animal  bones,  which  consist  of  from  24  to  30 %  of  animal 
substance  and  70  to  76,%  of  "bone  earth,"  (or  when  fossil 
are  free  from  the  former),  are  largely  used  for  the  manufac- 


MINERALS  USED  AS  FERTILIZERS.  65 

ture  of  superphosphate.  The  bone-earth  consists  in  the  main 
of  tri-calcic  phosphate  with  from  one  to  two  per  cent,  of  cal- 
cium fluorid  (much  as  in  natural  apatite),  a  small  amount  of 
magnesic  phosphate,  and  about  4  to  6,%  of  calcic  carbonate. 
Bone  meal  can  therefore  supply  to  plants  both  phosphoric  acid 
and  nitrogen,  and  the  presence  of  the  latter  has  been  largely 
the  cause  of  a  material  overestimate  of  its  efficacy  as  a  fertil- 
izer in  the  past.  \Yagner's  and  Maerker's  experiments  have 
shown  that  at  least  in  sandy  soils  poor  in  humus,  it  cannot  be 
considered  an  adequate  source  of  phosphoric  acid  for  annual 
crops,  and  that  in  these  soils  its  immediate  effects  are  almost 
wholly  due  to  its  nitrogen-content.  The  slow  availability  of 
the  phosphoric  acid  renders  it  unprofitable  as  a  source  of  the 
latter,  outside  of  the  heavier  lands  with  abundance  of  humus ; 
in  "sour"  lands  (notably  on  meadows)  bone  meal  produces 
its  best  results.  In  soils  naturally  calcareous,  or  in  such  as 
have  received  heavy  dressings  of  lime  either  as  carbonate  or  in 
the  caustic  condition,  the  manurial  effects  of  bone  meal  are 
seriously  diminished.  Nagaoka  ( Bull.  Coll.  Agr.  Tokyo,  Vol. 
6,  No.  3)  shows  that  the  crop  of  rice  fertilized  with  bone  meal 
was  reduced  to  less  than  half  when  limed,  and  that  the  phos- 
phoric acid  taken  up  by  the  crop  was  reduced  to  one-sixth.  In 
any  case  it  is  most  important  that  bone  meal  should  be  as  finely 
ground  as  possible,  as  in  the  case  of  the  phosphorites;  and  this 
can  best  be  done  when  it  has  first  been  freed  from  fats  by  boil- 
ing with  water,  and  then  steamed  under  pressure.  It  can  then 
also  be  most  readily  converted  into  superphosphate. 

The  phosphate  minerals  and  the  fertilizers  manufactured 
therefrom  are  of  primary  importance  to  agriculture.  The 
phosphoric-acid  content  of  soils  is  mostly  very  small,  and  only 
a  fraction  of  it  is  usually  in  an  immediately  available  form. 
Hence  for  permanent  productiveness,  and  especially  for  in- 
tensive farming  or  gardening,  a  cheap  supply  of  phosphate 
fertilizers  is  of  first  importance  in  all  soils  and  climates. 

Other  phosphate  minerals  occur  frequently,  but  as  a  rule 
only  in  small  amounts,  in  connection  with  the  ores  of  most 
metals.  The  only  ones  of  these  of  interest  to  agriculture  are 

J'h'ianitc  and  Dufrcnitc,  the  phosphates  respectively  of  the 
protoxid  and  peroxid  of  iron.  The  former  occurs  in  mineral 
deposits  as  small  blue  crystals,  or  more  frequently  as  blue 
5 


66  SOILS. 

earthy  masses  or  streaks,  in  the  substrata  of  rich  alluvial 
ground  (Louisiana,  California).  Dufrenite  sometimes  results 
directly  from  the  oxidation  of  the  protoxid  mineral,  which  then 
turns  greenish  and  finally  brown.  Unfortunately  these  miner- 
als, rich  as  they  are  in  phosphoric  acid,  cannot  readily  be  util- 
ized as  sources  of  phosphate  fertilizers,  because  of  the  difficulty 
of  getting  rid  of  the  iron.  Their  occurrence  usually  suggests 
the  presence  of  abundance  of  phosphoric  acid  in  the  soil.  But 
that  which  is  actually  combined  with  the  iron  oxids  is  prac- 
tically unavailable  to  plants;  especially  so  in  the  case  of  the 
peroxid  compound,  the  formation  of  which  is  a  common 
source  of  loss  of  phosphoric  acid  when  soils  rich  in  iron  are 
submerged  for  any  length  of  time;  a  point  which  is  discussed 
below  (chapt.  13). 

Among  the  iron  phosphate  minerals,  may  also  be  mentioned 
"  bog  ore,"  which  results  from  the  reductive  maceration  of 
swamped  ferruginous  soils,  and  accumulates  in  the  subsoils 
and  in  the  bottom  of  swamps  or  moors,  forming  "  moorbed- 
pan  "  ;  a  dark  brown,  rather  soft  mass,  which  is  sometimes  used 
as  an  iron  ore,  especially  since  the  invention  of  the  "  basic 
process  "  of  iron  smelting,  one  of  the  products  of  which  is 
the  phosphate  or  Thomas  slag.  (See  above). 

Nitrate  of  Soda  or  Chile  saltpeter. — This  mineral  being 
(like  all  nitrates)  easily  soluble  in  water,  can  only  occur  in 
regions  nearly  or  quite  destitute  of  rainfall.  Such  is  the  case 
in  the  Plateau  of  Tarapaca  in  Northern  Chile,  where  it  occurs 
in  large  quantities;  it  is  likewise  found,  but  to  much  smaller 
extent,  in  Nevada,  southern  California,  Egypt  and  India.  By 
far  its  most  extended  occurrence  is  that  in  Chile,  where,  to- 
gether with  common  salt,  it  fills  cavities  and  crevices  in  a 
gravelly  clay  that  forms  the  surface  of  a  plateau  from  three  to 
six  thousand  feet  above  the  sea.  It  is  never  pure,  but  always 
mingled  with  a  large  proportion  (up  to  $0%  and  over)  of 
common  salt;  also  some  Glauber's  salt  (sulfate  of  soda)  and 
some  sodic  perchlorate  and  iodid ;  hence  it  forms  an  important 
commercial  source  of  iodine. 

The  mixed  mineral  mass,  called  "  Caliche,"  when  taken  out  of  the 
ground  is  dissolved  in  water;  and  the  solution  boiled  down,  during 
which  process  the  common  salt  is  first  deposited  and  is  raked  out  of 


MINERALS  USED  AS  FERTILIZERS.  67 

the  pans ;  the  nitrate  is  afterward  farther  purified  by  crystallization. 
As  brought  into  commerce  for  agricultural  purposes  it  constitutes  a 
moist  gray  saline  mass,  somewhat  resembling  common  salt,  of  which 
substance  it  usually  contains  a  few  per  cent ;  occasionally  also  a  small 
amount  of  sodic  perchlorate  (which  acts  injuriously  on  vegetation). 
Aside  from  its  use  as  a  fertilizer,  Chile  saltpeter  serves  for  the  man- 
ufacture of  nitric  acid ;  and  either  directly,  or  after  previous  transform- 
ation into  potassic  nitrate,  for  that  of  gunpowder. 

The  Chilean  locality  is  the  only  one  from  which  the  commercial 
article  is  derived  ;  the  deposits  elsewhere  are  too  limited  in  extent  to 
compete  commercially  with  the  South  American  product.  Caliche 
ranging  as  high  as  8or/0  of  nitrate  of  soda  has  been  sent  to  the  writer 
from  the  Colorado  Desert  in  Southern  California,  but  the  exact  locality 
of  occurrence  has  not  been  divulged.  Extended  areas  of  clay  hills 
impregnated  with  nitrates  exist  in  the  Death  Valley  region  of  California, 
but  in  the  absence  or  extreme  scarcity  of  water  in  that  region,  it  is 
doubtful  whether  these  impregnations  can  be  made  practically  available. 
Another  locality  is  that  near  White  Plains,  Nevada,  where  Caliche 
averaging  about  S°%  purity  is  found  in  cavities  and  crevices  of  a  reddish 
volcanic  rock.  The  rainfall  in  this  region  is  so  slight  that  the  greater 
part  of  the  dust  or  sand  blown  about  by  the  wind  consists  of  Glauber's 
salt.  Here  also,  as  in  Chile,  the  niter  deposits  appear  to  be  restricted  to 
within  a  short  distance  from  the  surface,  and  the  total  amount  thus 
far  observed  appears  to  be  insufficient  to  encourage  large-scale  ex- 
ploitation. 

Origin  of  Nitrate.  Deposits.- — The  probable  origin  of  these  niter 
deposits  has  given  rise  to  a  great  deal  of  discussion,  and  a  wide  differ- 
ence of  opinion  exists  as  to  the  source  from  which  the  nitrogen  may 
reasonably  be  supposed  to  have  been  derived.  According  to  the 
present  state  of  our  knowledge,  it  must  be  presumed  that  its  sources 
have  been  organic,  and  that  the  niter  has  been  produced  by  the  activity 
of  the  same  bacteria  which  now  produce  nitrates  in  our  soils,  rendering 
the  nitrogen  of  humus  available  to  plants.  But  it  is  by  no  means  clear 
what  that  organic  material  could  have  been  ;  for  at  the  present  time 
the  plateau  of  Tarapaca  is  almost  wholly  destitute  of  vegetation,  if  not 
of  animal  life.  The  latest  and  apparently  most  reasonable  suggestion 
is  that  of  Kunfze,  who  calls  attention  to  the  fact  that  the  vicunas  and 
llamas  which  are  at  home  in  this  portion  of  the  Andes,  and  are  known 
to  have  roamed  over  that  region  in  countless  herds,  have  the  curious 
habit  of  always  depositing  their  manure  in  one  and  the  same  place 


68  SOILS. 

whenever  at  liberty.  Each  herd  of  these  animals  has  its  definite  dung- 
ing place  at  some  convenient  point.  That  such  herds  have  existed  in 
the  region  from  time  immemorial  is  obvious  from  historical  as  well  as 
collateral  evidence ;  and  as  their  manure  accumulated,  its  nitrification 
would  progress  rapidly  under  the  prevailing  arid  conditions.  The  com- 
mon salt  would  naturally  be  derived  from  the  urine  and  excrements, 
and  the  alkaline  salts  which  exist  throughout  this  region  as  the  products 
of  soil  decomposition,  would  be  quite  sufficient  to  account  for  the 
alkaline  bases  in  the  caliche.  On  the  other  hand,  the  presence  of 
iodine  points  to  seaweeds  as  the  organic  source. 

Intensity  of  Nitrification  in  Arid  Climates. — Of  the  efficacy 
of  nitrification  under  arid  conditions  abundant  evidence  may 
be  found  within  the  State  of  California.  In  the  alkali  lands 
of  southern  California  the  nitrates  of  soda,  lime  and  magnesia 
are  almost  universally  present ;  they  form  at  times  as  much  as 
one-fifth  and  even  more  of  the  entire  mass  of  alkali  salts,  and 
in  one  case  the  total  amount  in  the  soil  has  been  found  to  reach 
two  tons  per  acre,  with  an  average  of  twelve  hundred  pounds 
over  ten  acres.  In  the  plains  of  the  San  Joaquin  Valley,  spots 
strongly  impregnated  with  niter  are  found,  especially  under  the 
shadows  of  isolated  oak  trees,  where  the  cattle  have  been  in  the 
habit  of  congregating  for  a  long  time ;  a  case  quite  analogous 
to  that  supposed  by  Kuntse  to  exist  in  the  Chilean  locality. 
Of  course  it  is  only  in  arid  climates  that  the  accumulation  of 
nitrates  can  usually  occur;  for  in  the  region  of  summer  rains 
the  nitrates  formed  during  the  warm  season  will  inevitably  be 
washed  into  the  subdrainage,  unless  restrained  by  absorption 
by  the  roots  of  vegetation.  The  heavy  losses  occasionally 
occurring  from  this  cause  in  the  course  of  a  rainy  winter  on 
summer-fallowed  land  have  been  amply  demonstrated  by  many 
investigations. 

POTASH  MINERALS. — By  far  the  most  abundant  occurrence 
of  potash  in  the  earth's  crust  is  that  in  silicates  and  notably  in 
orthoclase  or  potash  feldspar,  which  contributes  so  largely  to 
soil-formation.  But  in  the  absence  of  any  economically  suc- 
cessful artificial  method  for  producing  potash  compounds  from 
feldspars  on  a  commercial  scale,  almost  the  entire  supply  of 
potash  salts  was,  until  a  comparatively  late  period,  derived  from 
plant  ashes,  viz.,  the  "  potashes  "  of  commerce.  At  the  same 


MINERALS  USED  AS  FERTILIZERS.  69 

time,  almost  the  entire  demand  for  alkalies  for  industrial  uses 
bore  upon  the  same  product,  until  the  invention,  toward  the  end 
of  the  last  century,  or  LcBlaiic's  process  for  the  manufacture 
of  soda  from  common  salt ;  for  until  that  time,  soda  in  the 
various  forms  in  which  it  was  imported  from  the  Orient  or 
prepared  from  seaweed  ashes,  was  a  comparatively  costly  pro- 
duct. LeBlanc's  invention  was  most  timely  in  that  it  very 
quickly  diminished  materially  the  production  of  potashes 
which,  in  view  of  the  increased  demand  for  alkalies  for  in- 
dustrial uses,  seriously  threatened  the  depletion  of  agricultural 
lands,  and  of  woodlands  as  well,  of  one  of  its  most  essential 
ingredients.  Yet  as  there  are  many  industrial  uses  in  which 
soda  cannot  replace  potash,  the  manufacture  of  potashes  con- 
tinued to  a  greater  or  less  extent,  as  no  other  available  source 
except  the  ashes  of  land  plants,  was  then  known.  The  pro- 
duction of  potassic  chlorid  from  the  mother-waters  of  sea  salt 
in  the  spontaneous  evaporation  of  sea  water  for  the  manu- 
facture of  common  salt,  was  on  too  small  a  scale  to  influence 
materially  the  manufacture  of  potashes. 

Discoi'cr\  of  Stassfurt  Salts. — The  depletion  of  potash  had 
become  so  serious  a  matter  in  the  agricultural  lands  of  Europe, 
that  for  a  time  much  research  was  bestowed,  and  prizes  offered 
for  an  economical  method  of  producing  potash  salts  from  feld- 
spar, on  a  commercial  scale.  But  the  problem  had  not  been 
satisfactory  solved  when,  in  the  year  1860,  attention  was  called 
to  the  fact  that  the  saline  deposits  overlying  certain  large 
rock-salt  beds  that  had  been  developed  by  borings  near  Stass- 
furt in  Prussia,  contained  so  large  a  proportion  of  potash  salts, 
as  to  render  their  purification  and  conversion  into  fairly  pure 
sulphate  and  chlorid  technically  feasible.  The  impulse  having 
been  given,  the  potash  industry  dcveloj>ed  rapidly  in  that 
region  as  well  as  in  the  adjacent  portions  of  Saxony,  where  the 
same  formation  underlies;  the  production  of  "Stassfurt 
Salts  "  rapidly  assumed  a  greater  development  than  that  of  the 
rock-salt  which  had  originally  prompted  the  enterprise,  and 
numerous  additional  boreholes  demonstrated  an  unexpectedly 
wide  extension  of  the  same  beds.  At  the  present  time,  in  con- 
sequence of  such  development,  the  manufacture  of  potashes 
from  plant  ash  has  almost  ceased,  outside  of  Canada  and 
Hungary;  and  the  production  of  potash  salts  in  the  Stassfurt 


70  SOILS. 

region  now  supplies  the  demand  of  the  entire  world,  both  for 
industrial  and  agricultural  purposes. 

The  cheapening  of  potash  as  a  fertilizer  has  rendered  pos- 
sible the  profitable  cultivation  of  large  areas  of  land  which 
were  naturally  too  poor  in  that  substance  for  ordinary  cul- 
tures; and  has  likewise  rendered  possible  the  restoration  to 
general  culture  of  lands  that  had  ceased  to  produce  adequately, 
on  account  of  the  depletion  caused  by  long-continued  cropping. 
It  has  likewise  served  to  intensify  agricultural  production 
wherever  desired;  and  between  this  supply  and  that  of  phos- 
phoric acid  from  the  phosphorites  (see  above),  and  the  dis- 
covery of  the  nitrogen-absorbing  power  of  leguminous  plants, 
which  can  be  used  for  green-manuring,  farmers  have  been 
enabled  to  dispense,  in  many  regions,  with  the  production  and 
use  of  stable-manure,  which  until  then  had  been  considered  an 
indispensable  adjunct  to  agriculture  everywhere.  Even 
within  the  last  fifty  years  it  was  proclaimed  by  high  authority 
in  Germany  that  stable-manure  constituted,  as  it  were,  the 
farmer's  raw  material,  from  which  he  manufactured  the  var- 
ious products  of  the  field  through  the  intervention  of  the 
plant-producing  power  of  the  soil. 

Origin  of  the  Potash  Deposits. — The  manner  in  which  this  accumu- 
lation of  potash  salts  has  been  formed  deserves  explanation.  It  is 
abundantly  evident  that  nearly  all  deposits  of  rock-salt  thus  far  known 
have  been  formed  by  the  evaporation  of  sea-water  at  times  when  bays 
or  arms  of  the  sea  were  cut  off  from  open  communication  with  the 
ocean.  The  composition  of  sea-water  has  already  been  given  and 
discussed  (chap.  2,  p. 26)  ;  and  by  the  slow  evaporation  of  sea-water  on 
a  small  scale  we  can  quite  successfully  imitate  the  phenomena  observed 
in  natural  rock-salt  deposits.  When  sea-water  is  heated  a  slight  deposit 
of  lime  carbonate  (usually  containing  a  little  ferric  oxid  and  silica)  is 
soon  formed  ;  and  a  corresponding  thin  deposit  of  ferruginous  limestone 
is  commonly  found  at  the  base  of  rock-salt-bearing  deposits.  Next 
above  this  we  almost  invariably  find  a  deposit  of  gypsum,  sometimes  of 
great  thickness  ;  in  the  artificial  evaporation  of  sea-water  the  same  thing 
occurs  so  soon  as  the  brine  has  reached  a  certain  degree  of  concen- 
tration. It  constitutes  the  major  portion  of  the  "  panstone  "  of  salt- 
boilers.  Next  above  follows  a  deposit  of  rock-salt,  at  base  somewhat 
mixed  with  gypsum  ;  its  thickness  varies  greatly  according  to  circum- 
stances. Above  it  lie  the  potash  salts. 


MINERALS.  USED  AS  FERTILIZERS  7I 

In  the  manufacture  of  sea-salt  by  evaporation  in  shore  lagoons  or 
"  saltpans,"  the  solution  remaining  after  the  salt  has  been  deposited 
(known  as  "mother-waters,"  or  "bittern"  ),  of  course  remains  on  the 
surface  of  the  salt  unless  allowed  to  drain  off,  as  is  done  in  the  process 
of  manufacture.  When  not  drained  off,  the  water  gradually  evaporates, 
and  there  remains  a  saline  crust  of  a  composition  exactly  resembling 
that  of  the  upper  layers  at  Stassfurt,  containing  a  large  proportion  of 
potash  salts. 

If  it  be  asked  why  the  Stassfurt  salts  are  not  found  overlying  every 
rock-salt  deposit  in  the  world,  the  answer  is  that  in  a  great  many  cases 
the  concentrated  mother-waters  have  had  an  opportunity  to  flow  off 
from  the  surface  of  the  rock-salt  by  the  action  of  tides,  the  inflow  of 
fresh  water  from  the  land  or  from  other  causes.  Their  presence 
therefore  depends  upon  the  fulfilment  of  accidental  conditions  not 
nearly  always  realized  in  the  natural  evaporation  of  sea-water,  but 
which  happened  to  occur  on  a  very  large  scale  in  that  portion  of  the 
North-European  continent. 

Nature  of  the  Salts.— -The  potash  is  present  in  the  Stassfurt  salts  in 
the  form  of  complex  sulfates  and  chlorids  containing,  besides,  sodium, 
calcium  and  magnesium  in  various  proportions  and  modes  of  com- 
bination. The  most  abundant  of  the  potassic  chlorid  minerals  is  car- 
nallite,  a  hydrous  chlorid  of  potassium  and  magnesium.  The  chlorids 
characterize  chiefly  the  upper  portions  of  the  deposit,  the  sulfates 
the  lower. 

Kainit. — Of  the  products  derived  from  the  Stassfurt  salt 
industry  for  agricultural  use,  the  two  requiring  special  con- 
sideration are  "  kainit,"  a  natural  mixture  of  the  several  chlo- 
rid minerals  in  varying  proportions;  and  "high-grade  sul- 
fate."  Being  a  natural  product,  "  kainit  "  is  the  cheapest 
source  of  potash  available  to  the  farmer;  but  on  account  of 
its  variability  in  composition  it  must  be  sold  and  purchased  on 
guaranteed  assay.  On  account  of  its  large  content  of  chlorin 
it  is  not  desirable  in  the  production  of  certain  crops,  especially 
in  'the  arid  region,  where  alkali  soils,  and  even  those  not  visi- 
bly alkaline,  often  contain  already  large  amounts  of  chlorin. 
Moreover,  kainit  usually  contains  a  considerable  proportion 
of  common  salt.  For  the  arid  region  therefore  the  sulfate 
is  generally  preferable,  although  it  is  somewhat  higher  in 
price  for  the  same  amount  of  potash.  The  potash  content  of 


72  SOILS. 

commercial  kainit  (calculated  as  K2O)  ranges  from  16  to 
35%,  while  the  sulphate  frequently  ranges  from  80  up  to 
95%  of  the  pure  sulfate;  thus  costing  materially  less  in 
freight  charges  than  the  lower-grade  kainit.  Its  potash  con- 
tent ranges  from  43  to  over  50%  of  K2O. 

Potash  Salts  in  Alkali  Soils. — The  sulfates  and  chlorids  of 
potassium,  however,  occur  not  only  in  connection  with  rock- 
salt  deposits,  but  are  also  found  in  the  alkali  soils  of  the  arid 
region.  They  are,  in  fact,  never  absent  where  such  salts 
occur  at  all,  and  their  percentage  in  the  total  of  salts  ranges  all 
the  way  from  about  4  to  as  much  as  20%  of  potash  sulphate. 
In  numerous  cases  it  has  been  found  that  the  content  of  this 
salt  to  the  depth  of  four  feet  amounts  to  from  1200  to  1500 
pounds  per  acre.  In  such  lands,  of  course,  additional  fertiliza- 
tion with  potash  salts  is  totally  uncalled  for,  the  more  as  such 
soils  invariably  contain,  besides  the  water-soluble  potash,  an 
unusually  large  percentage  of  the  same  in  the  form  of  easily 
decomposable  silicates,  or  zeolites. 

Farmyard  or  Stable  Manure. — In  connection  with  the  sub- 
ject of  mineral  fertilizers,  it  will  be  proper  to  discuss  briefly 
the  uses  and  special  merits  of  stable  manure,  composts,  etc. 
Up  to  within  the  last  century,  these  were  practically  the  only 
fertilizers  known  and  used,  and  the  exclusive  use  of  this 
manure  might  have  continued  indefinitely  but  for  the  dis- 
covery that  as  time  progressed,  stable  manure  and  with  it 
grain  crops,  for  the  production  of  which  it  was  necessary,  be- 
came less  and  less  in  amount,  so  as  to  threaten  bread  famines. 
The  cause  of  this  diminution  was,  of  course,  the  incomplete- 
ness of  the  return  of  the  soil-ingredients  taken  off  by  the  crops, 
when  these  were  exported  to  feed  the  cities  or  foreign  coun- 
tries. Thus  the  attention  of  chemists,  and  notably  that  of 
Liebig,  was  attracted  to  the  solution  of  the  problem  of  keeping 
up  production  even  with  an  insufficient  supply  of  stable  ma- 
nure; and  the  discovery  of  the  use  of  mineral  fertilizers  was 
the  result  of  their  activity. 

The  chemical  composition  of  stable  manure  does  not,  alone, 
suffice  to  explain  its  remarkable  efficacy  and  the  difficulty 
of  replacing  it  by  any  other  material.  The  composition  of 
manure  of  course  differs  not  only  with  different  animals  but 


MINERALS  USED  AS  FERTILIZERS. 


/3 


also  with  the  different  feeds  consumed  by  them ;  but  the  aver- 
age composition  of  farmyard  manure  is  approximately  given 
thus  by  Wolff  and  others : 

ANALYSES  OF   VARIOUS   FARMYARD   MANURES. 


Water  

1. 

7I.OO 

2. 

7C.OO 

3. 

79.00 

4. 

79-95 

5. 

72.33 

Dry  Matter     

29-00 

2  S  OO 

21  OO 

20.01; 

27-67 

Ash  ingredients  

A  4O 

c8o 

6  so 

5-87 

Potash  

O  f.2 

J's 
OOT. 

o  so 

0.84  * 

0-69 

Lime    

O  C7 

o  70 

0.88 

0-85 

Magnesia  

O  14 

0.18 

0.18 

0*14 

Phosphoric  acid   

0.  21 

0.26 

0.30 

0.40 

0*30 

Ammonia  

O'O2 

Total  Nitrogen  

O.4  C 

o.  t;o 

o  sS 

0.78 

0*46 

1.  Average  composition  of  fresh  farm  manure     (Wolff). 

2.  Average  composition  of  moderately  rotted  farm  manure     (Wolff). 

3.  Average  composition  of  very  thoroughly  rotted  farm  manure   (Wolff). 

4.  Mixed  cow  and  horse  manure  from  a  bed  two  feet    thick,  accumulated  during 
the  winter  in  a  large  covered  yard,  and  packed  solid  by  the  tramping  of  cattle    (The 
analysis  by  F.  K.  Furry). 

5.  "Box  Manure,"   consisting  of   mixed    manure  of  bullocks,  horses,  and  pigs 
(Way,  Royal  Agric.  Soc.  Journ.,  1850,  II.,  769). 

It  is  thus  seen  that  the  percentage  of  the  important  plant- 
foods  in  stable  manure  are  minute  when  compared  with  those 
commonly  found  in  "  commercial  "  fertilizers.  Nor  are  they 
so  much  more  available  for  plant  absorption  than  the  latter; 
a  very  large  proportion  is  not  utilized  at  all  the  first  year,  and 
unless  the  amount  applied  is  very  large  it  hardly  carries  the 
supply  needed  for  the  usual  crops. 

It  is  now  well  understood  that  its  efficacy  is  largely  due  to 
the  important  physical  effects  it  produces  in  the  soil.  It  helps 
directly  to  render  heavy  clay  soils  more  loose  and  readily  till- 
able. If  well  "  rotted  "  or  cured  it  also  serves  to  render 
sandy,  leachy  soils  more  retentive  of  moisture;  and  the  humus 
formed  in  its  progressive  decay  imparts  to  all  soils  the  highly 
important  qualities  discussed  later  on  (chapt.  8).  More  than 
this,  the  later  researches  have  shown  that  stable  manure  acts 
perhaps  most  immediately  upon  the  bacterial  activity  in  the 
soil,  greatly  increasing  it  not  only  directly  by  the  vast  numbers 
of  these  organisms  it  brings  with  it,  but  also  in  supplying  ap- 
propriate food  for  those  normally  existing  in  the  soil  (see 

1  And  soda. 


74 


SOILS. 


chapt.  9).  In  so  doing  it  serves  indirectly  to  render  the  soil 
ingredients  more  available,  and  to  impart  to  the  soil  the  loose 
condition  required  in  a  good  seed-bed — a  "  tilth  "  which  can- 
not be  brought  about  by  the  operations  of  tillage  alone. 

The  only  possible  substitute  for  the  use  of  stable  manure  is 
found  in  green-manuring  with  leguminous  crops  conjointly 
with  the  use  of  commercial  or  mineral  fertilizers.  Unless  this 
is  done  the  use  of  the  latter,  alone,  ultimately  leads  to  a  deple- 
tion of  humus  substances,  which  renders  the  acquisition  of 
proper  tilth  by  the  seed-bed  impossible,  and  causes  a  com- 
pacting of  the  surface  soil  which  no  tillage  can  remedy. 

Proper  method  of  using  stable  manure  in  humid  and  arid 
climates. — In  the  humid  region  it  is  a  common  practice  to 
spread  the  stable  manure  on  the  surface  of  the  fields  and  leave 
it  there  without  any  special  operation  to  put  it  into  the  soil; 
trusting  to  the  rains,  earthworms  and  subsequent  tillage  for 
its  being  brought  into  adequate  contact  with  the  roots ;  it  is 
rarely  plowed  in.  In  the  arid  region  this  mode  of  using  it  is 
impracticable ;  it  would  remain  on  the  surface  indefinitely  with- 
out advancing  in  its  decay  because  of  the  dryness,  and  unless 
plowed  in  very  deep  the  ordinary,  strawy  manure  would  ruin 
the  seed-bed  by  rendering  it  too  pervious  to  the  dry  air,  thus 
preventing  germination.  Much  of  this  valuable  material  has 
therefore  been,  and  to  some  extent  is  still  being  burnt,  thus 
causing  a  severe  depletion  of  the  land,  both  of  humus  and  of 
mineral  plant-food.  The  best  way  to  deal  with  stable  manure 
in  the  arid  regions  is  to  thoroughly  rot  or  cure  it  before  putting 
it  on  the  land,  and  then  plowing  it  in.  To  do  this  of  course  it 
must  be  put  in  piles  and  wetted  regularly;  a  procedure  which 
at  the  high  prices  of  labor  is  thought  to  be  too  expensive,  but 
which  in  the  end  would  be  found  eminently  profitable,  unless 
green-manuring  is  regularly  done.  The  very  small  proportion 
of  humus  generally  present  in  arid  soils  renders  this  precaution 
indispensable,  if  production  and  proper  tilth  is  to  be  main- 
tained. The  saving  of  stable  manure  and  of  all  composting 
material,  even  if  less  needful  as  a  means  of  supplying  plant- 
food  in  the  rich  soils  of  the  arid  regions,  is  fully  as  essential 
in  order  to  maintain  the  humus  supply. 


MINERALS  UNESSENTIAL  OR  INJURIOUS  TO  SOILS.       75 

(B.)   MINERALS   UNESSENTIAL  OR   INJURIOUS   TO   SOILS. 

The  minerals  heretofore  mentioned  contribute  to  soil  forma- 
tion either  one  or  several  ingredients,  important  to  plant  growth 
either  by  their  mechanical  or  chemical  action.  It  remains  to 
consider  some  not  intrinsically  desirable,  but  frequently  pres- 
ent in  certain  soils,  which  should  be  known  to  the  farmer  in 
order  that  he  may  be  enabled  to  counteract  or  remove  their 
injurious  effects.  Leaving  aside  such  as  are  of  only  casual  or 
rare  occurrence,  the  following  may  be  mentioned  as  among 
those  which  not  unfrequently  affect  soils  desirable  for  culture 
to  such  extent  as  to  make  them  unavailable  for  general  farming 
purposes  : 

Iron  Pyrites;  sulphid  of  iron  containing  two  molecules  of 
sulphur  to  one  of  iron  ;  a  mineral  exceedingly  common  in  de- 
posits of  metallic  ores,  and  whose  deceptive  gold-like  color  has 
caused  it  to  be  mistaken  for  gold  so  often  as  to  cause  it  to  be 
designated  as  "  fool's  gold  "  among  miners.  While  it  fre- 
quently does  contain  some  gold  and  is  often  associated  with 
valuable  ores,  it  is  practically  valueless  when  occurring  outside 
of  mineral  veins,  in  rock  masses;  and  more  especially  in  sedi- 
mentary rocks,  such  as  sandstones,  limestones,  shales  and  clays. 

When  present  in  soils  it  sometimes  becomes  a  source  of 
trouble  to  the  farmer,  because  in  contact  with  air  it  is  soon 
transformed  into  ferrous  sulfate  or  copperas,  which,  like  the 
carbonate  referred  to  above,  is  injurious  to  plants.  Sometimes 
indeed  iron  pyrites  is  actually  formed  in  badly-drained  soils 
alongside  of  the  carbonate  of  iron,  when  much  sulfate  (such 
as  gypsum)  is  present;  and  then  its  injurious  effects  subside 
more  slowly  than  do  those  of  the  carbonate  (  see  above,  p. 


Recognition  of  Iron  pyrites.  —  The  mineral  is  easily  recognized  by  its 
golden  or  brass-yellow  tint  ;  the  latter  color  being  the  one  most  com- 
monly shown  in  the  "  sulphur  balls  "  occurring  in  marls  or  soft  lime- 
stones. A  very  easy  test  is  to  pulveri/.e  it  and  then  heat  it  on  a  shovel 
over  a  fire,  when  it  will  soon  itself  take  fire,  burning  with  a  blue  sulphur 
flame,  and  upon  more  complete  roasting,  leaving  behind  a  red  powder, 
viz.,  "  Venetian  red"  or  red  ochre;  that  is,  ferric  oxid.  In  clays  it 
commonly  occurs  in  large,  well-defined  cubes,  which  do  not  readily 
form  copperas  but  rather  become  covered  with  a  crust  of  limonite 
or  brown  iron  ore. 


76  SOILS. 

When  a  subsoil  is  found  to  contain  pyrites,  or  when  "sulfur 
balls  "  have  been  accidentally  introduced  with  dressings  of 
marl,  the  remedy  is  thorough  and  persistent  aeration  of  the 
material.  In  the  case  of  marls  nothing  more  need  be  done ;  but 
in  that  of  ill-drained  subsoils  it  is  best  to  add  lime  in  moderate 
dressings,  to  accelerate  the  transformation  into  ferric  hydrate 
or  iron  rust,  and  gypsum ;  whereby  the  copperas  becomes  not 
only  innocuous  but  adds  two  beneficial  ingredients  to  the  soil. 
The  same  policy  will  render  available  manure  or  other  materials 
which  have  been  disinfected  by  means  of  solution  of  copperas. 

Halite  (rock-salt),  or  common  salt,  has  already  been  men- 
tioned as  to  its  occurrence  in  connection  with  the  Stassfurt 
potash  salts  (see  above,  page  71);  but  as  rock-salt  it  rarely 
exerts  any  injurious  influence  upon  lands.  It  is,  however,  a 
common  ingredient  of  seashore  lands,  and  is  also  present  to  a 
certain  extent  in  the  alkali  lands  of  the  arid  countries.  While 
it  is  true  that  occasionally  small  quantities  of  common  salt  are 
used  as  an  ingredient  in  fertilization,  its  usefulness  in  that 
direction  is  exceedingly  subordinate ;  and  it  is  far  more  gener- 
ally to  be  considered  as  an  injurious  ingredient  of  all  culti- 
vatable  soils  whenever  present  to  a  larger  extent  than  a  few 
hundredths  of  one  per  cent.  It  is  usually  considered  that  one- 
fourth  of  one  per  cent  of  common  salt  renders  lands  unfit  for 
most  culture  plants.  Only  a  few,  such  as  asparagus,  the  beet, 
the  saltbushes  and  some  others,  succeed  when  it  is  present  in 
this  or  in  larger  amounts.  In  the  case  of  sea  water  it  is  usually 
accompanied  by  a  still  more  injurious  ingredient,  magnesic 
chlorid  or  bittern;  which  is  detrimental  to  plant  growth  in 
much  smaller  quantities  than  the  common  salt  itself. 

Recognition  of  Common  Salt. — The  presence  of  common  salt  may, 
as  a  rule,  be  detected  by  the  taste,  well-known  to  every  one ;  when  this 
taste  is  very  intense  or  somewhat  bitterish,  it  indicates  the  presence  of 
bittern.  The  presence  of  salt,  however,  is  easily  verified  without  the 
use  of  chemical  reagents,  by  slowly  evaporating  some  of  the  clear  water 
leached  from  the  soil  in  a  clean  silver  spoon.  If  the  last  few  drops  are 
allowed  to  evaporate  spontaneously,  it  will  be  easy  to  distinguish,  even 
with  the  unaided  eye,  the  square,  cubical  crystals,  sometimes  combined 
into  cross-shape,  which  are  characteristic  of  common  salt.  It  is  always 
an  unwelcome  addition  to  the  land,  and  as  its  action  cannot  be  neu- 


MINERALS  UNESSENTIAL  OR  INJURIOUS  TO  SOILS.        77 

tralized  in  any  way,  it  can  be  gotten  rid  of  only  by  leaching-out.  This 
process  is  usually  accomplished  in  seashore  lands  by  the  action  of  rain, 
or  by  the  overflow  of  fresh-water  streams,  after  the  tide  has  been  ex- 
cluded by  means  of  drains  provided  with  check-valves  to  prevent  the 
inflow  of  tidewater;  or  else  by  underdrainage,  and  flooding  when 
possible. 

Mirabilitc,  (Glauber's  salt)  or  sulfate  of  soda,  exists  not 
un frequently  in  the  soils  of  the  arid  region  and  sometimes  en- 
crusts extended  areas  of  lowlands  during-  the  dry  season. 
When  present  in  the  soil  it  will  commonly  be  seen  blooming 
out  on  the  surface  after  a  rain,  in  light,  feathery,  needle-shaped 
crystals,  sometimes  to  such  an  extent  that  it  can  be  collected  by 
the  handful.  Subsequently,  when  wafted  by  the  wind,  it  is 
reduced  to  a  fine  white  dust,  which  constitutes  a  goodly  pro- 
portion and  sometimes  the  entire  mass  of  the  "  alkali  dust  " 
that  is  so  annoying  on  the  plains  of  Nevada,  and  in  the  desert 
regions  generally,  during  the  hot  summer.  Near  White  Plains, 
Nevada,  it  forms  a  thick  layer  of  "white  sand,"  in  which  the 
foot  sinks  deeply,  and  which  is  carried  about  by  the  wind  with 
great  ease. 

Glauber's  salt  is  never  a  desirable  soil-ingredient.  It  is 
largely  produced  as  a  by-product  in  several  industries,  but 
cannot  be  utilized  for  agricultural  purposes  to  any  extent.  It 
is,  however,  much  less  injurious  to  plant  growth  than  common 
salt;  according  to  experience  in  California  it  may  be  considered 
about  three  times  less  so.  It  constitutes  the  major  portion 
of  what  is  commonly  known  as  "  white  alkali,"  which  is  well 
known  to  be  much  less  injurious  to  crops  than  the  "  black  " 
kind,  which  contains  carbonate  of  soda. 

Troiia  and  I'rao  arc  natural  forms  of  carbonate  of  soda  or 
salsoda.  Like  Glauber's  salt,  it  commonly  occurs  as  a  surface 
efflorescence  or  crust  in  dry  or  desert  regions;  either  from  the 
evaporation  of  standing  water,  as  in  the  case  of  the  soda  lakes 
of  Nevada.  Hungary  and  Kgypt,  or  as  an  efflorescence  on  the 
surface  of  the  soil,  as  in  the  western  United  States.  Mexico 
("urao").  North  Africa  ("trona"),  and  at  many  points  in 
the  Old  Continent.  In  the  United  States  it  is  commonly 
known  as  "  black  alkali."  because  of  the  black  spots  formed  on 
the  surface  by  evaporation;  practically  the  same  name 


78  SOILS. 

("kara")  is  given  it  in  Arabia  and  Asia  Minor,  whence  im- 
pure soda  has  long  been  imported  into  Europe ;  while  in  north 
India  it  forms  part  of  the  "  reh  "  salts  that  incrust  large  areas 
(usar  lands)  in  the  Indo-Gangetic  plain. 

The  natural  mineral  always  contains  an  excess  of  carbonic  acid  over 
the  "  normal  "  salt,  nearly  in  the  proportion  of  four  parts  of  carbonic 
dioxid  to  three  of  soda ;  it  is  sometimes  designated  as  sesqui-carbonate. 
In  hot  sunshine  it  may  lose  most  of  this  excess  for  a  time ;  while  within 
the  soil  itself  it  may,  in  presence  of  abundant  carbonic  acid,  become 
temporarily  converted  wholly  into  hydrocarbonate  or  "  bicarbonate," 
which  is  less  corrosive  than  the  monocarbonate  or  common  salsoda. 

Injury  caused  in  soils. — Like  common  and  Glauber's  salt, 
carbonate  of  soda  is  always  an  unwelcome  soil  ingredient ; 
more  so,  in  fact,  than  either  of  the  other  two,  since  less  than  a 
tenth  of  one  per  cent  is  sufficient  to  render  certain  soils 
wholly  untillable,  by  the  deflocculation  or  puddling  of  the  clay; 
at  the  same  time  rendering  it  impervious  to  water.  It  is  by 
far  the  most  injurious  ingredient  that  ordinarily  occurs  in 
otherwise  good,  arable  soils;  for  in  addition  to  the  physical 
effect  just  mentioned,  it  dissolves  the  humus-substance  of  the 
soil,  forming  an  inky-black  solution  which,  especially  when 
evaporating  on  the  surface  and  forming  black  spots,  has  given 
rise  to  the  popular  name  of  "  black  alkali."  As  will  be  more 
fully  explained  hereafter,  wherever  such  is  the  case,  the  first 
step  necessary  toward  reclamation  is  the  transformation  of  the 
carbonate  of  soda,  at  least  in  part,  into  the  relatively  innocu- 
ous sulfate,  by  means  of  gypsum  in.  the  presence  of  water; 
while  carbonate  of  lime  remains  in  the  soil. 

In  its  direct  action  on  the  plants  themselves,  soda  is  also 
most  injurious;  as  when  accumulated  to  any  extent  near  the 
surface  by  evaporation  it  will  corrode  the  root-crown  or  stem, 
and  sometimes  completely  girdle  the  same,  destroying  the 
bark.  Farther  details  on  this  subject  are  given  in  chap- 
ter 22. 

Epsomitc,  or  Epsom  salt,  or  sulfate  of  magnesia,  is  another 
one  of  the  water-soluble  minerals  frequently  found  efflorescent 
on  the  surface  of  the  ground ;  more  commonly  in  saline  sea- 
shore lands  than  in  the  alkali  region  proper,  although  it  is 


MINERALS  UNESSENTIAL  OR  INJURIOUS  TO  SOILS.        79 

rather  common  in  the  northeastern  portion  of  the  arid  region 
of  the  United  States.  Whether  on  the  soil  surface  or  in  the 
crevices  of  rocks,  its  needle-shaped,  feathery  crystals  greatly 
resemble  those  of  Glauber's  salt,  but  are  readily  distinguished 
by  the  more  intensely  bitter  taste.  Epsom  salt  is  frequently 
the  last  remnant  of  sea-salts  left  in  the  soil  after  reclamation. 
Though  probably  somewhat  more  injurious  to  plant  growth 
than  Glauber's  salt,  the  mineral  Kieserite,  one  of  the  Stassfurt 
salts  and  consisting  essentially  of  Epsom  salt,  is  sometimes 
used  as  an  application  to  calcareous  lands  instead  of  gypsum, 
and  with  good  results.  Yet  gypsum  is  usually  the  safer,  and 
equally  effective. 

Borax  (bi-borate  of  soda)  occurs  much  more  rarely  than 
the  salts  just  described;  most  frequently  in  certain  portions  of 
California,  forming  part  of  the  "'  alkali  "  in  the  soil.  It  is 
injurious  to  plant  growth,  but  is  as  readily  dealt  with  as  is  the 
carbonate  of  soda,  by  dressings  of  gypsum,  whereby  inert 
borate  of  lime  is  produced. 

It  is  hardly  necessary  to  say  that  saline  waters  containing 
any  of  the  above  salts  in  notable  amounts  must  be  used  for 
irrigation  very  cautiously.  The  measures  to  be  observed  in  this 
respect  will  be  discussed  later. 


PART  SECOND. 

PHYSICS  OF  SOILS. 


CHAPTER  VI. 

PHYSICAL  COMPOSITION  OF  THE  SOILS. 

As  has  already  been  stated  (chapt.  i,  p.  10),  the  general 
physical  constituents  of  soils  are  rock  powder  or  sand  and  silt, 
more  or  less  decomposed  according  to  the  nature  of  the  orig- 
inal rocks;  cla\,  the  product  of  the  decomposition  of  feldspars 
and  some  other  silicates;  luinnis,  the  complex  product  of  the 
decomposition  of  vegetable  and  animal  matters  on  and  in  the 
soil  mass;  as  well  as  vegetable  matter  not  yet  humified.  Each 
of  these  several  constituents  must  now  be  considered  more  in 
detail.  Since  clay  is  the  substance  whose  functions  and 
quantitative  proportions  influence  most  strikingly  the  agri- 
cultural qualities  of  land,  it  should  be  first  discussed. 

Clay  as  a  Soil  Ingredient. 

The  plasticity  and  adhesiveness  of  clay,  together  with  the 
extreme  fineness  of  its  ultimate  particles  (said  to  reach  the 
1-25000  of  an  inch),  explains  its  great  importance  as  a 
physical  soil  ingredient.  It  serves  to  hold  together  and  im- 
part stability  to  the  tlocculent  aggregates  of  soil  particles  that 
compose  a  well-tilled  soil;  for  without  clay  the  sand  would 
collapse  into  close-packed  single  grains  so  soon  as  dried,  and 
loose  tilth  would  be  impossible.  Sand  drifts  illustrate  this 
condition. 

On  the  other  hand,  the  fineness  of  the  particles  serves  to 
render  clay  very  retentive  of  moisture  as  well  as  of  gases  and 
of  solids  dissolved  in  water,  imparting  these  important  prop- 
erties to  soils  containing  it;  while  coarse  sandy  soils  are  often- 
times so  deficient  in  them  as  to  render  them  unadapted  to  any 
useful  culture,  despite  the  presence  of  an  adequate  supply  of 
plant-food. 

\Yhen  to  these  essential  physical  properties  of  clay,  there  is 
added  the  fact  that  usually  the  clay-substance  as  it  exi.-ts  in 

83 


84  SOILS. 

soils  contains  the  most  finely  pulverized  and  most  highly  de« 
composed  portions  of  the  other  soil-minerals,  and  therefore  the 
main  part  of  the  available  mineral  plant-food,  it  is  easy  to 
understand  why  soils  containing  a  good  supply  of  clay  should 
be  ca-lled  and  considered  "  strong  "  land  by  the  farmers  of  all 
countries.  "  Poor"  clay  soils  are  exceptional;  but  sometimes 
the  clay  content  reaches  such  a  figure  that  the  difficulties  of 
tillage  render  them  too  uncertain  of  production  for  profitable 
occupation. 

Amount  of  Colloidal  Clay  in  Soils. — Any  and  all  of  the  kinds 
of  clay  mentioned  (p.  57)  as  occurring  naturally  may,  of 
course,  enter  into  and  form  part  of  soils.  But  as  the  amount 
of  true,  plastic  clay  substance  contained  in  them  is  very  in- 
definite, it  becomes  necessary,  in  order  to  classify  soils  in  re- 
spect to  their  tillableness,  to  ascertain  more  definitely  the 
amount  of  pure,  or  nearly  pure,  colloidal  clay  substance  con- 
tained in  the  several  classes  of  soils  ordinarily  recognized  and 
mentioned  in  farming  practice.  That  this  determination  can 
at  best  be  only  approximate,  is  obvious  from  the  fact  mentioned 
above  (chapt.  4,  p.  59),  that  pure  kaolinite  itself  is  not  plastic, 
and  only  becomes  so  by  the  indefinite  comminution  and  hydra- 
tion  it  experiences  in  the  processes  of  soil-formation.  As  the 
progress  of  this  process  is  also  indefinite,  the  same  soil  con- 
taining particles  ranging  from  the  finest  to  the  chalky  scales 
of  pure  kaolinite,  the  drawing  of  a  line  must  be  more  or  less 
arbitrary  and  empirical. 

From  numerous  experiments  and  comparisons  made,  the  writer  has 
been  led  to  place  the  limits  of  "  plastic  clay  "  at  and  below  such  grain 
sizes  as  will  remain  suspended  (afloat)  in  a  water  column  eight  inches 
high,  during  24  hours.  To  go  beyond  this  point  in  the  examination  of 
soils  for  practical  purposes,  would  render  such  examinations  so  labor- 
ious and  hence  so  rare,  that  this  kind  of  work  would  be  practically  ex- 
cluded from  ordinary  practice.  According  to  this  view  the  following 
percentages  of  such  "  clay  "  correspond  approximately  to  the  designa- 
tions placed  opposite  : 

Very  sandy  soils 5  to    3$  c^ay 

Ordinary  sandy  lands .     .     .     3.0  to  10%     " 

Sandy  loams 10.0  to  15%     " 

Clay  loams 15.01025%      " 

Clay  soils 25.0  to  35%     " 

Heavy  clay  soils     ....  35.0  to  45%  and  over. 


PHYSICAL  COMPOSITION  OF  SOILS.  85 

It  must  be  distinctly  understood,  however,  that  these  figures  make  no 
claim  to  accuracy  or  invariability.  For,  the  tilling  qualities  of  a  soil 
containing  one  and  the  same  amount  of  such  "  clay  "  may  be  very 
materially  modified  according  to  the  kind  and  amount  of  each  of  the 
several  grain-sizes  of  rock  powder  or  sand  they  contain. 

Influence  of  fine  poivders  on  plasticity  and  adhesiveness. — An 
admixture  of  a  large  amount  of  fine  powders  diminishes  mater- 
ially the  adhesiveness  of  a  clay  soil,  even  though  it  may  render 
it  even  more  "  heavy  "  in  tillage;  while  the  admixture  of  coarse 
sand,  even  in  very  considerable  proportions,  does  not  greatly 
influence  the  adhesiveness  of  the  clay.  The  latter  alone  can- 
not therefore  serve  as  a  proper  guide  or  basis  for  the  classifica- 
tion of  soils  in  respect  to  tillage;  we  must  also  take  into  con- 
sideration the  nature  and  amount  of  the  several  granular  sedi- 
ments mixed  with  it. 

Moreover,  the  nature  and  especially  the  adhesiveness  of  the 
clay  substance  as  obtained  by  analysis  may  vary  considerably 
in  the  presence  of  a  very  large  amount  of  the  finest  grain-sizes; 
among  which  ferric  hydrate  or  iron  rust  is  especially  apt  to 
accumulate  predominantly  in  the  clay,  considerably  increasing 
its  apparent  weight  and  greatly  diminishing  its  adhesiveness.1 
In  strongly  ferruginous  soils,  therefore,  it  becomes  necessary 
to  take  into  special  consideration  the  amount  of  the  ferric 
hydrate  or  rust  which  accumulates  in  the  clay  substance.  The 
presence  of  large  amounts  of  humus  or  vegetable  mold  also 
influences  materially  the  adhesiveness  and  physical  properties 
of  the  clay  obtained  by  the  method  described,  although  most  of 
it  remains  with  the  finer  powdery  sediments  or  grain-sizes. 
There  are.  besides,  other  colloidal  or  at  least  amorphous  sub- 
stances present  in  all  soils,  such  as  silicic,  aluminic  and  zeolitic 
hydrates,  which  are  all  non-plastic,  and  yet  sufficiently  fine  to 
form  part  of  the.  "  clay  "  obtained  as  above  specified. 

Despite  these  imperfections.  (  which  however  can  in  a  mea^- 
ure  be  taken  into  consideration  in  judging  of  a  soil's  tilling 
qualities  by  its  clay  content),  the  figures  given  in  the  above 
table  approximate  much  more  nearly  to  a  tangible  basis  for 
such  estimate,  than  the  utterly  indefinite  mixtures  which  under 
the  older  methods  of  analysis  have  been,  and  still  are  to  some 
extent,  used  as  a  basis  for  soil  classification  by  writers  on 
agriculture. 

1  This  fact  emphasizes  the  impossibility  of  explaining  the  plasticity  and  adhesive- 
ness of  clay  simply  as  a  function  of  fineness  of  strain. 


86  SOILS. 

Rock  Pozvder;  Sand,  Silt  and  Dust. 

The  powdery  (sandy  and  silty)  constituents  of  soils  usually 
constitute  the  greater  part  of  their  mass;  and  the  proportions 
present  of  the  several  grades  of  fineness  exert  a  most  decisive 
influence  upon  their  cultural  qualities,  and  very  commonly 
upon  their  agricultural  value  also.  It  is  needless  to  add  that 
the  kind  of  mineral  of  which  they  consist  or  from  which  they 
\vere  formed,  is  also  of  great  importance  in  determining  the 
quality  of  soils  from  the  standpoint  of  the  chemist,  with  respect 
to  their  content  of  mineral  plant- food. 

WEATHERING  IN   HUMID  AND  ARID  REGIONS. 

Sands  of  the  Humid  Regions. — As  has  already  been  stated, 
"  sand  "  is  usually  understood  to  be,  in  the  main,  quartz  more 
or  less  finely  pulverized,  generally  intermingled  with  a  few 
grains  of  other  minerals.  With  this  understanding,  since 
quartz  is  practically  inert  with  respect  to  plant  nutrition,  it 
follows  that  soils  consisting  mainly  of  this  substance  contain 
but  little  plant-food ;  hence  the  common  expression  "  poor, 
sandy  land,"  the  outcome  of  the  experience  had  in  Europe  and 
in  the  Eastern  United  States,  and  which  until  recently  has  been 
held  to  be  of  general  application.  The  "  sands  of  the  desert  " 
have,  both  in  ordinary  life  and  in  poetry,  always  stood  as  the 
symbol  of  sterility. 

Thus  the  sandy  lands  (  "  sand  hammocks  "  )  of  Florida,  the  (long- 
leaf)  pine  lands  of  the  Gulf  States,  the  "  pine  barrens  "  of  New  Jersey 
and  of  Michigan,  are  noted  both  for  their  sandy  soils  and  their  sterility 
after  brief  cultivation ;  necessitating  fertilization  within  a.  few  years 
from  the  time  of  occupation.  In  Europe,  the  "  Heide "  (heather) 
soils  of  northeastern  Germany  are  of  the  same  cultural  character. 

Sands  of  the  Arid  Regions. — The  experience  of  arid  coun- 
tries however,  has  long  ago  shown  that  some  very  sandy  lands 
— c.  g.,  such  as  form  the  oases  of  the  north  African  deserts- 
may  be  extremely  productive  when  irrigated,  and  also  of  con- 
siderable durability.  Actual  experience  and  close  investiga- 
tion given  this  subject  in  the  arid  regions  of  the  United  States 
has  fully  demonstrated  that  lands  appearing  to  the  casual  ob- 


PHYSICAL  COMPOSITION  OF  SOILS.  87 

server  to  be  hopelessly  sterile  sandy  deserts,  very  commonly 
prove  to  be  even  more  productive  than  the  more  clayey  lands  of 
the  same  regions.  Examination  of  the  sand  shows,  in  these 
cases,  that  instead  of  mere  grains  of  quartz,  the  minerals  of  the 
parent  rock,  partially  decomposed,  themselves  constitute  a 
large  proportion  of  the  sandy  mass.  But  in  the  regions  of 
deficient  rainfall,  as  has  already  been  stated,  (p.  47)  the 
formation  of  clay  (kaolinization)  is  exceedingly  slow;  hence 
the  decomposition  of  the  rock  powder  results  in  the  production 
of  predominantly  pulverulent  instead  of  clayey  soils.  But  the 
mineral  plant-food  is  not  on  that  account  less  available,  pro- 
vided other  physical  conditions  necessary  for  the  success  of 
plant  growth  are  fulfilled.  Among  these  moisture  stands 
foremost ;  hence  the  relative  proportions  of  the  several  grain- 
sizes  are  of  vital  importance,  since  upon  this  depends  to  a  great 
extent  the  proper  supply  and  distribution  of  moisture,  without 
which  no  amount  of  plant-food  will  avail.  Moreover,  the 
finest  and  most  highly  decomposed  powder  is  the  portion  from 
which  the  roots  draw  their  chief  food-supplies. 

The  point  last  mentioned  is  well  shown  in  the  results  obtained  by 
Dr.  R.  H.  Loughridge,  from  the  analysis  of  each  of  the  several  grain- 
si/es  into  which  he  had  resolved  a  very  generalized  soil  of  the  State  of 
Mississippi,  representing  a  very  large  land  area  in  that  State  as  well  as 
in  Tennessee  and  Louisiana.  The  details  of  this  investigation  are 
given  farther  on  ;  but  summarily  it  may  be  stated  that  he  found  prac- 
tically the  whole  of  the  acid-soluble  mineral  plant-food  accumulated 
within  the  portion  of  the  soil  the  fineness  of  whose  grains  was  below 
.025  millimeters  (one-thousandth  of  an  inch)  ;  ingredients  so  fine  as 
to  be  wholly  impalpable  between  the  fingers.  Moreover,  two-thirds  of 
the  total  amount  was  found  in  the  portion  described  above  as  "clay." 
It  is  thus  readily  understood  why  clay  soils  are  in  the  regions  of  summer 
rains  commonly  designated  as  "strong"  lands. 

The  corresponding  later  investigations  of  Kud/inski  (Ann.  Agr.  Inst. 
Moscow,  Vol.  9,  No.  2,  pp.  172-234:  Kxp.  Sta.  Record,  Dec.  1904, 
p.  245)  and  of  Ma/urenko  (Jour.  Kxp.  Landw.  1904,  pp.  73-75  ;  Kxp't 
Stn.  Record,  Dec.  1004,  p.  344)  fully  corroborate  Loughridge's  con- 
clusions, for  typical  soils  of  Kuropean  Russia. 

Ill  the  arid  or  irrigation  regions,  however,  the  case  is  dif- 
ferent, for  the  reason  that  much  of  the  decomposed  rock- 


88  SOILS. 

substance  remains  adherent  to  the  surface  of  the  larger  grains, 
and  plastic  clay  is  formed  to  a  much  less  extent.  Much  avail- 
able plant-food  may  therefore,  in  arid  lands,  be  present  even  in 
rather  coarsely  sandy  soils  almost  devoid  of  clay;  such  as  in 
humid  climates  would  he  likely  to  be  found  wholly  barren. 
(See  chapt.  19). 

PHYSICAL  ANALYSIS  OF  SOILS. 

Use  of  Sieves. — Down  to  a  certain  point  the  separation  of 
the  soil  into  its  several  grain-sizes  may  be  accomplished  by 
means  of  sieves.  We  may  thus  separate  coarse  gravel  from 
fine  gravel  and  from  sand ;  and  the  latter  may  itself  be  sepa- 
rated into  several  sizes  by  the  same  means.  This  presupposes, 
of  course,  that  the  soil  has  been  previously  prepared  for  the 
purpose  by  crushing  the  lumps  consisting  of  aggregates  of 
finer  particles,  that  in  the  operation  of  tillage  would  again  be 
resolved  into  their  fine  constituents,  or  be  penetrated  by  roots. 
But  this  preparation  of  the  soil  for  sifting  must  not  be  carried 
beyond  the  point  mentioned,  for  a  grain  consisting  of  particles 
somewhat  firmly  cemented  together  will  under  ordinary  con- 
ditions play  in  the  soil  precisely  the  same  part  as  a  solid  sand- 
grain,  and  must  not  therefore  be  broken  up,  if  the  soil  is  to  be 
examined  in  its  natural  condition.  The  pressure  of  the  fingers 
or  of  a  rubber  pestle  is  as  far  as  trituration  should  go.  The 
disintegration  of  these  compound  particles  by  means  of  acids, 
as  prescribed  and  practiced  by  the  French  soil  chemists,  may 
wholly  change  the  physical  nature  of  the  soil  by  the  breaking- 
up  of  mechanical  aggregations  which  in  the  usual  course  of 
tillage  would  remain  intact.  This  is  especially  true  of 
strongly  calcareous  soils,  and  particularly  those  containing 
calcareous  sand. 

The  sieves  used  for  this  purpose  should  not  be  ordinary  wire  sieves, 
but  should  have  bottoms  of  sheet  brass  perforated  by  round  holes  of 
the  various  diameters  desired,  of  fractions  of  inches,  or  preferably  of 
millimeters.  For  the  finer  grain  sizes,  silk  bolting  cloth  is  used  by  the 
U.  S.  Bureau  of  Soils. 

In  the  sifting  process  it  will  be  found  that  so  soon  as  the  finer  grain- 
sizes  of  the  sand  are  approached,  the  sieve  fails  to  act  satisfactorily ; 
the  more  so,  the  more  clay  was  originally  contained  in  the  material. 


PHYSICAL  COMPOSITION  OF  SOILS.  89 

The  fine  particles  flock  together,  forming  little  pellets,  which  refuse  to 
be  separated  by  the  sieve.  This  difficulty  can,  of  course,  be  partly 
overcome  by  previously  separating  the  clay  from  the  sand  by  means  of 
water,  as  detailed  above ;  but  even  then  it  will  be  found  that  so 
soon  as  the  grain-sizes  fall  much  below  ^  of  an  inch  (i  millimeter) 
the  same  difficulty  is  experienced,  so  long  as  the  sand  is  dry.  By 
playing  a  small- stream  of  water  upon  the  sieve,  however,  all  the  parti- 
cles beyond  the  ^J-^  of  an  inch  may  be  successfully  separated  from  the 
coarser  portion  ;  and  for  many  practical  purposes  the  separation  need 
be  carried  no  farther. 

Use  of  Water  for  Separating  Finest  Grain-Sizes. — The  scientific 
investigator,  however,  must  of  necessity  proceed  to  separate  the  finer 
grain-sizes  from  each  other,  since,  as  will  presently  be  shown,  they 
influence  the  tilling  qualities  of  the  soil  to  a  much  greater  degree  than 
do  the  coarser  particles.  Such  farther  separation  can  be  accomplished 
only  by  the  aid  of  water. 

Subsidence  Method. — \Yhen  a  snvill  amount  of  soil  is 
stirred  up  in  water,  and  is  afterward  allowed  to  stand  for  some 
time,  the  different  grain-sizes  will  settle  consecutively  in  ac- 
cordance with  their  sixes  (or  weights);  the  smallest  ones 
settling  latest,  and  the  clay  only  remaining  suspended,  as 
stated  above.  So  long,  however,  as  any  considerable  amount 
remains  suspended  in  the  water,  the  latter  is  not  only  denser 
hut  especially  more  viscid  than  if  the  clay  were  absent.  In 
order  therefore  to  obtain  correct  results  by  any  method  in- 
volving the  use  of  water,  it  is  necessary  to  remove  the  clay  he- 
fore  proceeding  to  the  separation  of  the  granular  sediments. 
This,  as  has  been  already  stated,  is  approximately  accom- 
plished by  allowing  the  soil,  when  diffused  in  water  after 
proj>er  disintegration,  to  settle  for  24  hours  from  a  column  of 
water  200  mm.  high,  whereby  all  grain-sixes,  of  and  above  .01 
mm.  diameter  are  removed  from  the  turbid  liquid.  This 
sedimentation  is  then  repeated  until  after  24  hours  the  water 
becomes  clear.  The  clay  is  then  determined  in  the  "  clay 
water"  by  evaporation  or  precipitation;  the  granular  sedi- 
ments may  then  he  successfully  separated  by  sedimentation. 

The  L\  S.  I'ureau  of  Soils  uses  for  the  separation  of  clay, 
instead  of  subsidence  for  24  hours,  the  more  expeditious  pro- 
cess of  contrifugiug  the  turbid  soil  water  in  appropriate  glass 
cylinders,  hv  the  aid  of  an  electric  motor;  and  thus  in  a  rel- 


Cjo  SOILS. 

atively  short  time  obtains  "  clay  "  in  which  the  upper  limit  of 
size  is  one-half  of  that  mentioned  above,  viz.,  .005  mm.  But 
for  the  costliness  of  the  appliances  required,  including  the 
entire  time  of  an  operator,  this  method  of  separating  the  clay 
would  undoubtedly  be  preferable  to  the  elimination  by  sub- 
sidence; the  more  as  a  more  minute  grain-size  for  the  clay 
group  is  thus  secured. 

The  separation  of  the  clay  having  been  accomplished,  the 
various  sizes  of  silt  and  sand  may  be  separated  by  again  sus- 
pending them  in  water;  and  interrupting  the  settling  process  at 
stated  times,  the  grain-sizes  corresponding  to  definite  velocities 
in  settling  may  be  segregated  and  weighed.  When  this  process 
of  settling  and  decanting  is  carefully  and  repeatedly  carried 
out,  very  good  results  are  obtained. 

Hydraulic  Elutriation. — The  sedimentation  (or 
"beaker")  method,  long  practiced  in  the  arts  is, 
however,  quite  tedious,  requiring  the  constant 
close  attention  of  a  skilled  observer.  The  desired 
results  may,  in  the  writer's  judgment,  be  more 
conveniently  obtained  by  the  hydraulic  method, 
whenever  no  very  large  volume  of  work  of  this 
kind  is  required  to  be  done  at  once. 

When  instead  of  allowing  the  soil  to  settle  in 
quiet  water,  the  latter  is  used  as  an  ascending  cur- 
rent of  regularly  graded  velocities,  it  is  clear  that 
the  soil  particles  will  be  carried  off  by  this  current 
in  exact  conformity  with  their  several  sizes  (or 
strictly  speaking,  volume-weights)  ;  and  when 
maintained  in  such  a  current  for  a  sufficient  length 
of  time,  the  entire  quantity  of  the  sediment  cor- 
responding to  the  prevailing  velocity  will  be  car- 
ried away.  It  is  of  course  easy  to  ascertain  to 
what  grain-sizes  certain  velocities  of  the  upward 
Hotmtor.  8'current  (regulated  by  a  stopcock  with  arm  moving 
on  a  graduated  scale)  correspond,  and  to  regulate  accordingly 
the  intervals  between  the  different  velocities  to  greater  or  less 
detail,  as  may  be  desired.  A  number  of  instruments  have  been 
devised  for  this  purpose, 

ScJwne's  Elutriator  is  the  one  commonly  used  in  Europe; 


PHYSICAL  COMPOSITION  OF  SOILS. 


91 


in  it  the  upward  current  ascends  in  a  conical  glass  tube,  (see 
figure  6)  entering  through  a  narrow,  curved  inlet  tube,  in  which 
the  soil  sample  is  kept  agitated  by  the  current  itself.  The 
objection  to  this  plan  is  twofold :  first,  the  narrow,  curved 
inlet-tube  is  readily  clogged  by  the  soil  mass  at  the  lower 
velocities,  which  are  thereby  changed,  so  that,  unless  a  very 
small  amount  of  soil  only  is  employed,  the  whole  mass  is  not 
kept  properly  stirred ;  second,  the  circulating  currents  brought 
about  by  the  conical  shape  of  the  tube  cause  the  sediment-par- 


FK..  7. — The  Churn  Klutri.itor  i  Hilgnrd's)  for  the  physical  analysis  of  soils. 

tides  t<>  coalesce  into  complex,  larger  ones  (floccules).  which 
will  then  settle  down  rind  fail  to  pass  over  at  the  current- 
velocity  corresponding  to  their  individual  component  parts. 

Churn  l:Jiitn\it<»'  ;^////  Cylindrical  Tube. — The  errors  just 
alluded  to  are  obviated  by  an  arrangement  devised  by  the 
writer,  in  which  a  rapidly-revolving  ^tirrer.  placed  at  the  base 
of  a  cylindrical  tube  in  which  the  washing  process  is  conducted 


92 


SOILS. 


and  which  eliminates  counter-currents,  continually  disintegrates 
these  compound  particles,  and  thus  enables  the  entire  quantity 
of  the  sediment  corresponding  to  the  prevailing  current-velo- 
city to  pass  off  with  a  comparatively  slight  expenditure  of  time 
on  the  part  of  the  operator  (see  figure  7).  A  wire  screen  in- 
terposed between  the  churn  and  cylindrical  glass  tube  prevents 
communication  of  the  whirling  motion  to  the  column.  As  the 
apparatus  works  automatically,  the  analyst  has  only  to  observe 
from  time  to  time  whether  or  not  the  turbidity  near  the  top  of 
the  tube  has  disappeared ;  and  as  the  sediment  accumulates  at 
the  bottom  of  the  tall  receiver  bottle,1  no  harm  is  done  if  the 
attendant  should  neglect  to  change  the  velocity  in  time,  except 
ttyat  water  will  run  to  waste. 

The  conical  relay  glass  below  the  churn  serves  to  retain  the 
coarser  grades  of  sediments  which  are  not  concerned  in  the 
velocities  employed  in  the  elutriator  tube,  and  thus  prevents 
injurious  attrition.  But  these  sediments  can  at  any  time  be 
stirred  up  by  the  incoming  current  and  brought  into  the  wash- 
ing tube  if  desired.  In  the  same  manner  the  passing-off  of 
the  finer  sediments  can  be  materially  accelerated  by  running 
off  rapidly  about  two-thirds  of  the  turbid  column  of  water 
every  twenty  minutes. 

It  should  be  fully  understood  that  prior  to  attempting  such 
separation,  the  "  colloidal  clay  "  must  first  be  removed  by  the 
subsidence  or  centrifugal  method,  since  otherwise  much  larger 
grain-sizes  may  be  carried  off  at  a  given  velocity. 

Voder's  Centrifugal  Elutriator. — A  very  ingenious  instru- 
ment which  combines  the  elutriation  and  sedimentation  pro- 
cesses into  one,  has  been  devised  by  P.  A.  Yoder,  of  the  Utah 
Expt.  Station.  The  elutriator  bottle  is  placed  in  a  centrifuge 
driven  by  an  electric  motor;  it  is  closed  by  a  glass  stopper 
carrying  a  delivery  tube  to  a  short  distance  above  the  bottom 
of  the  elutriator  bottle,  as  well  as  an  outflow  tube  ending  at  the 
base  of  the  stopper;  the  latter  also  carries  a  funnel  coinciding 
with  the  center  of  rotation.  Into  this  funnel  flows  gradually 

1  The  figure  given  of  this  elutriator  in  Bulletin  NTo.  24,  on  physical  soil  analysis, 
published  by  the  U.  S.  Bureau  of  Soils,  shows  as  the  receiver  a  bottle  entirely  too 
low  to  insure  the  complete  retention  of  the  sediments  by  settling.  The  receiving 
bottle  should  not  be  less  than  twelve  inches  high  and  five  inches  wide. 


PHYSICAL  COMPOSITION  OF  SOILS. 


93 


the  muddy  water  containing  the  soil  in  suspension ;  and  the  rate 
of  its  flow,  together  with  the  velocity  of  rotation,  determines 
the  size  of  the  sediment-granules  that  will  be  deposited  in  the 
slack-water  below  the  mouth  of  the  delivery  tube.  The  muddy 
soil-water  is  kept  agitated  in  a  funnel-shaped  reservoir  by  air- 
bubbles  from  a  constant-pressure  chamber. 

While  the  principle  of  this  instrument  is  good,  it  is  quite 
complicated  and  the  results  obtainable  from  it  in  practice  have 
not  as  yet  been  made  public.  The  inventor  claims  that  an 
analysis  may  by  its  means  be  completed  in  less  than  three 
hours. 

In  all  hydraulic  elutriators  a  provision  for  constant  press- 
ure in  the  reservoir  supplying  the  current  of  water  is  needed ; 
although  in  Scheme's  and  some  other  instruments  a  gradually 
decreasing  pressure  in  a  plain  reservoir  is  employed.  A  large 
glass  bottle  or  carboy  fitted  with  the  proper  tubes  so  as  to  con- 
stitute a  Mariotte's  bottle  ( in  which  the  air  enters  near  the 
bottom  of  the  vessel),  is  a  very  convenient  arrangement. 

Number  of  Sediments. — The  number  of  grain-sizes  or  sedi- 
ments into  which  the  soil  mass  is  to  be  segregated  is  of  course 
entirely  within  the  option  of  the  operator.  Experience  has 
shown  that  it  is  unnecessary  to  discriminate  very  closely  be- 
tween the  several  sixes  of  the  coarser  portion  of  the  sand,  such 
as  those  lying  between  one-fourth  and  one-half  of  a  millimeter. 
I'ut  below  this  point,  and  especially  between  one-tenth  of  a 
millimeter  and  the  clay,  a  proper  discrimination  becomes  very 
important.  The  series  first  devised  by  the  writer  in  1872  is 
based  upon  a  consecutive  doubling  of  the  velocities  of  the  cur- 
rent from  a  quarter  of  a  millimeter  per  second  to  thirty-two 
millimeters  per  second;  the  sediment  of  sixty-four  millimeter- 
velocity  corresponding  to  a  diameter  of  one-half  of  a  milli- 
meter, will  remain  in  the  clutriator.  Above  this,  as  before 
remarked,  the  sieve  (especially  when  aided  by  a  jet  of  water) 
effects  a  satisfactory  segregation. 

The  table  below  shows  the  elements  of  these  series  both  as 
regards  current-velocities  and  maximum  quartz-grain  diame- 
ters carried  off  by  each.  In  a  great  many  cases,  however,  it  is 
altogether  unnecessary  to  go  into  such  detail,  and  a  subdivision 
into  six  or  seven  divisions  is  quite  sufficient.  Such  a  sub- 


94 


SOILS. 


division,  based  upon  the  doubling  of  grain-sizes  instead  of 
current-velocities,  has  been  adopted  by  Prof.  Milton  Whitney, 
of  the  U.  S.  Department  of  Agriculture,  and  others. 

TABLE  OF  DIAMETERS  AND  HYDRAULIC  VALUES  OF  SEDIMENTS. 


Designation  of  materials. 

Velocity  per  sec- 
ond, or  hydraulic 
value. 

Maximum  dia- 
meter of  quartz 
grains. 

Grit  

Mm. 

(?) 

Mm. 
i—  -i 

(?) 
32-64 

1  6-72 

•5-i 

•So 

.-JO 

f 
Silt  

8-16 
4-8 

2-  4 

I.O-    2 

.  -5-  * 

..6 

.12 

.072 
.047 
.036 

Clay  

.25-0.5 
0.25 
*:  0.25 
<]  0.0023 

.025 
.Ol6 
.OIO 

Results  of  sucJi  analyses. — A  tabular  presentation  of  the  re- 
sults of  analyses  made  in  accordance  with  the  above  plan  will 
give  a  good  idea  of  the  differences  between  the  various  grades 
of  soils  recognized  in  farm  practice,  to  any  one  accustomed  to 
the  study  of  figures.  But  a  much  more  satisfactory  showing 
is  made  by  placing  the  several  grain-sizes  segregated,  into 
small  vials  or  tubes  of  identical  diameter  and  placing  them  in 
parallel  series  alongside  of  each  other.1  The  curves  formed 
by  the  surfaces  of  the  several  sediment-columns  in  each  series 
show  to  the  eye  very  strikingly  the  relations  of  the  several 
grades  of  soils  to  each  other,  and  suggest  at  once  that  while 
gentle  slopes  or  gently  undulating  curves  belong  to  soils  of 
intermediate,  loamy  character,  steep  grades  and  zigzags  show 
soils  of  extreme  types.  This  is  exemplified  in  the  subjoined 
Figures : 


1  Convenient  stands  for  this  purpose,  used  by  the  writer  since  1872,  may  be  cut 
from  L-shaped  moldings  of  wood,  such  as  can  be  readily  ordered  from  any 
planing  mill.  The  vials  can  be  cemented,  wired  or  tied. 


PHYSICAL  COMPOSITION  OF  SOILS. 


95 


Reddish  Loan  Soil 

Riv«rside 
California 


Diamcr«r6v      (in      Millimeters) 


FIG.  8 — Illustration  of  Results   of  Hydraulic   Klutriation,  showing  extremes  of  soil   texture,  and 
intermediate  loam. 


96 


SOILS. 


Sandy,  to  dm  So  ( I 

San  Bernardino   Valley 

al  if orniA 


Clay!  Silts  .        '         Sand*  I 

Dimeter*   ('in  Hilllroiter.  )  , 


.0251  .03*    .0471  .07i. 121.16 


FIG.  g. —  Illustration  of  Results  of  Hydraulic  Klutriation,  showing  Alluvial  Silts  and  Pine-Woods 
Soil. 

Physical  composition  corresponding  to  popular  designations 
of  Soil  quality. — The  subjoined  table  illustrates  the  physical 
composition  of  a  number  of  soils  from  the  State  of  Mississippi, 


PHYSICAL  COMPOSITION  OF  SOILS.  97 

selected  for  their  representative  character,  in  order  to  deduce 
therefrom  approximate  definitions  of  physical  character  corre- 
sponding to  popular  designations.  This  table,  published  in 
1873  m  accordance  with  results  obtained  during  the  two  pre- 
ceding years,  does  not  require  any  material  modification  on 
account  of  subsequent  investigations.  It  lacks,  however,  a 
characteristic  representative  of  the  predominant  soils  of  the  arid 
region,  viz.,  the  silty  soils  so  prevalent  in  dry  climates,  only 
approximately  represented  by  No.  165  of  the  table;  hence  two 
such,  from  California,  exemplifying  respectively  the  valley 
deposits  of  the  Sacramento  and  Colorado  rivers,  have  been 
added  to  the  list. 

It  must  not,  however,  be  understood  that  these  typical  soils 
necessarily  represent  correctly  the  physical  constitution  of  all 
soils  falling  under  the  same  popular  designation ;  for  we  are 
far  from  being  able  as  yet  to  predict  accurately  in  every  case  the 
tilling  qualities  of  a  soil  material  from  its  physical  composi- 
tion. To  do  this  it  would  be  necessary  not  only  to  know  with 
some  degree  of  precision  the  several  physical  coefficients  of  each 
of  the  several  grain-sizes,  and  perhaps  of  many  more  inter- 
mediate ones ;  but  we  would  also  have  to  construct  a  formula 
according  to  which  each  could  be  given  its  proper  weight  when 
present  in  varying  proportions,  and  of  varying  shapes,  surface 
condition,  and  material.  For  this  our  present  knowledge  is 
wholly  inadequate,  if  indeed  the  problem  is  not  beyond  the 
limits  of  mathematical  computation.  We  must  for  the  pres- 
ent at  least  be  satisfied  with  the  empirical  approximations 
afforded  us  by  the  constantly  increasing  number  of  such 
analyses,  correlated  with  farming  experience. 

Since  the  finest  grain-sizes  above  those  classed  as  "  clay "  do  not 
tend  to  "lighten"  soils,  but  even  to  render  them  more  intractable 
("  putty  soils"),  while  coarser  ones  gradually  change  the  dense  clay- 
texture  into  the  "  loamy,"  it  is  clear  that  in  between  there  must  be  a 
neutral  point,  some  grain  si/es  which  by  themselves  do  not  influence 
soil  texture  either  way.  Discussion  of  numerous  physical  analyses,  and 
some  direct  experiments,  have  led  the  writer  to  conclude  that  this  theo- 
retically neutral  grain-size  lies  at  or  near  the  diameter  of  .025  mm.,  or 
.5  mm.  hydraulic  value.  In  correlating  the  results  of  analysis  with  the 
tilling  qualities  of  the  soil  as  to  "  heaviness  and  lightness,"  therefore, 
that  grain-size  may  usually  be  left  out  of  consideration. 
7 


98 


SOILS. 


MISSISSIPPI  UPLANDS.  MISSISSIPPI  RIVER  BOTTOM.  CALIFORNIA. 

River  Deposit. 

• 
<o       -03  o3sia  ueg 

•*uo 

fn  tn  M  .r  -  n  —  v      o*    ^ 
—  «  —  r^  »^>  **>^  w     t^    o1 

S.   ^8 

3>     * 

0      -03  ojuauimDEg 

•O}U3lUEJDEg 

d  >o  r^  t^  «     -    *c 
m  -  n  \o  -    >O     5 

O        00 

i   * 

River  Deposit  Delta. 

•tr[  -JBJ  suituanbEU 

•diun[-pnj\[  ]S3Mt()nog 

O     «  oo  •*  CT-OO  *r  ->  sc  oo 
-     ovo-^ou-i^o-*-- 
o    i^i  f*j  »o  6  »«  c-oo  *oo 

8 
8 

•JBJ  amuisnbEU 

'SSl'J    }S3Ml]jnOg 

-     »  o1  m  JJoo"  «"  K  <£"  « 

00 

>d 

iy 

O        O    t^  N    rr,  U1QO     ^  O-  1 

_~~ 

g>        -03  EuioijEO3 
«   -riog  aSpi^j  -M2o(j 

-                t>  -TOO    O    O-  ""ivO    f^ 

fl      a^ 

O                «•>  -    -    •«•  <?•  O'OO    O 

g-      „« 

f~       '03  J3«oyung 
«   -jiosqng  puEjjuojj 

«     cr  "-  o  r-  o  t^  o-w  - 

-f        00    - 
O        ^O   fo 

O 

«            -03  etOUBJ 
•"'IPS  "IIV  ailpJEqEIpU, 

O         O     O    M    fl>O     T<1OC     fO  t^   r*:O 

K        £?n 

O      OOO-MO-C-CO-mo- 

00         %O    ft 

O^ 

!• 

1! 

5 

£       '03  3iuoqiEl3 
J?              -ssao'i 

•*-     r---fo»«t«t^>Ooo^30- 

6    odd--'  j«  d  UT^>  « 

^      oo  r-» 

tN.              "•      « 

&       *« 

a 

(3 

L    5 

o        '03  EusnbEssj 
«      -1103  joqsiiang 

O  »0        vO           «    t^sO    rrCC    r^  O*  O 

-  TT 

00           O           0    0    -    M    <100  00    T 
rrt  •*• 

8    ?r 

3?    - 

u 

!  • 

>, 

1     ' 

in 

0                "03  43dSEf 

S'-Iiosqng  MO||EM-3oH 

OO"-CS>OOOM    —    ^vOmr^*-O 

8    °£8 

d      •»  » 

5       - 

O---OOO«muiO'»-r-x 

«.           -03  «i«»v 
«   'itosqns  S[l!H  P»H 

r~     PtNO'OCT'OOmOwui 
O*      ^f^Ot^NOOOt^r*lfON 

CO 
»•        \C   *o 

_*_ 

vD         00    O 

5.      »  x 

0             '03  30JOJUOJ 
J?'JlOg    SpOOMJEJJ  X(fJ 

l«l  in                   **>00    «  \C   m  •*  "^OO 
fOM                     «-«-O-Oc->'» 

o  6             d  d  -  N  d--o  N  •'i 

oo'      S^ 

S:     °^ 

jj         '03  aojno^j 
•[losqng  auieaj 

O            «         OVO^*'^''"^M*O 
-             \O           «    N    O>  <^.OO  00    N    - 

M          d        d  «  fi  1^.06  r^»  u-i  f^ 

S\            M     "" 

CT-               '03  UO)U3fJ 

S  -riosqng  spuE'i  ajqEj, 

fo    r^  »*i  i^oo  *c  C->D  •*•  r^  o  o 
«     •*f}~t^t^r^N-C"^« 

U-i            ^f    — 
>D            N     - 

O       «cl«OOCir^r*^  »^\c    CT- 

g.  K^ 

£        -03  ajiafojE-j 
«      'Iiosqng  paojxQ 

O        d   O   m  t'.-C   r^-oc    r^- 

w>        C"  "1 

o 

g-       -03  miwg 

L  «     'I!°sqng  HIM  3QH 

f*10O    N    pnOO    n-^  *O    ^  t^*C    1^  t^ 

r^       c~  >^ 

I^       >C    •*• 

O0<0mm~0n>n  i^<o  r~.  o 

O- 

'  ~%           "°O  M'l^S 
N       'I!0S  II!H  3"!d 

»^.  0s  O    t^O   "i"    u-iiriC-r<    f<iu^ 
O  ri  •o   t^.  m  -   -   m-c   m  •*•  o-  •*• 

-B-    °^« 
S    "  " 

^>         -03  MESE5(31t]3 
•]IOg    SpOOMJE|  J 

O  vO    -    «-    ro  «    f^O    r^OO    r^  N  sC 
&•  O'OO    ^-ortO-O-OvCOO 

"     r^^ 
=§-     "r 

MON-»««r.^O-5J«^>^ 

«.          '03  jadsEf 
«  -Jiosqng  EuioqEHEX 

O-NOOO    ->OvD    OOO    030    -^-irivO 

>d  tioo  d  N  -  -  d  -  t^od  >A» 

J    C5: 

oo^     "03  o2uiuiot|si  T^ 
"     '^eiD-adW  3l»iA\ 

'S      °o  o  ?°§  q  o  -  o 
d       ddddoN-jj 

•s  arc 

00          C-  O 

o- 

CA  'JPXH) 
XJUOJSA 

•pUOD3S  J3J 

•S-lS)3Ull[|[Ji; 

•«-NvDOO-«-M-6dp'8 

«c  n-                               V  o 

V 

Hygroscopic  Moisture 

(+7  =  tO-f21°C)  

Ferric  Oxid  

•(SJSISUJ 

-HIM) 
jaiauiEiQ 

N    rxkO    w.  sD    O 

V  ~  2<  S^  "q'Jo'qoq^. 

c 
o      *> 

"«    "* 
|o| 

0    2 

•a                 :          >, 
•c         S                -         J 
O         w                  in          U 

PHYSICAL  COMPOSITION  OF  SOILS. 


99 


Number  of  soil  grains  per  gram. — It  is  of  some  interest  to 
consider  the  number  of  grains  of  different  sizes  that  may  be 
contained  in,  c.  g.,  a  gram  of  soil.  If  for  this  purpose  we  as- 
sume all  the  soil  grains  to  be  spherical,  \ve  shall  obtain  the 
minimum  figures,  for  most  other  shapes  will  pack  more  closely. 
King  (Physics  of  Agriculture,  p.  117)  calculates  such  figures 
for  different  grain-sizes,  assuming  the  density  to  be  that  of 
quartz  (2.65),  with  the  result  that  while  with  a  diameter  of  one 
millimeter  (1-25  inch)  the  number  of  grains  would  be  720, 
and  with  one-tenth  of  a  mm.  720,000;  if  made  of  the  finest 
particles  only,  viz.,  one  thousandth  of  a  mm.,  the  number 
would  be  720,000  billions.  Probably  few  of  the  clayey  soils 
we  ordinarily  deal  with  are  of  this  order;  it  is  doubtless 
approached  in  certain  fine  plastic  clays. 

Surface  afforded  by  various  grain-sizes. — The  amount  of 
surface  afforded  by  a  similar  amount  of  soil  must  naturally  be 
considered  in  this  connection,  since  upon  it  depends  not  only  the 
amount  of  moisture  which  the  soil  may  hold  in  the  form  of 
superficial  films,  but  also  the  extent  of  surface  upon  which  the 
weathering  agencies  as  well  as  the  root  hairs  of  plants  may  act. 
Quoting  again  from  King's  work,  we  find  on  the  same  premises 
given  above  for  the  number  of  grains,  that  their  surface  would 
in  the  case  of  grains  of  one  mm.  diameter  be  eleven  square  feet 
per  pound  (about  half  a  pint)  of  material;  while  in  the  case  of 
the  finest  grade  we  should  have  110,538  square  feet,  or  more 
than  two  and  a  half  acres. 

From  actual  experiments  made  with  the  flow  of  air  through 
various  soils,  King  calculates  that  while  in  ordinary  loam  soils 
the  total  surface  is  about  an  acre  per  cubic  foot,  in  fine  clay 
soils  it  rises  to  as  much  as  four  acres.  If  we  imagine  this 
large  surface  to  be  covered  with  even  a  very  thin  film  of  water, 
it  is  readily  seen  how  large  an  amount  may  be  present  in  a  cubic 
foot  of  moist  soil. 

E.  A.  Mitschcrlich  (Bodcnkunds  fur  I^and-und-I-'orstwirthe  ;  Berlin, 
1905)  attributes  to  the  surface  offered  by  the  soil  particles  supreme 
importance  in  determining  the  productiveness  of  soils.  According  to 
him  the  internal  soil-surface  determines  directly  the  ea^e  with  which 
roots  can  penetrate  the  soil  ;  and  he  proposes  the  determination  of  this 
factor  by  means  of  the  heat  produced  in  wetting  the  soil  (  '•  Benet- 


100  SOILS. 

zungswarme  "  ),  measured  in  a  calorimeter,  as  a  substitute  for  all  methods 
of  physical  soil  analysis,  which  are  vitiated  by  the  varying  shapes  and 
densities  of  the  particles ;  while  his  method  gives  directly  the  actual 
surface.  To  the  consumption  of  energy  required  by  difficult  penetra- 
tion he  attributes  most  of  the  differences  in  production,  and  hence  re- 
fers to  the  internal  soil-surface  as  governing  nearly  all  the  other  physi- 
cal factors.  The  introduction  of  many  arbitrary  assumptions,  and  the 
failure  to  show  that  the  admitted  inaccuracy  of  the  ordinary  mechanical 
soil  analyses  are  of  any  practical  importance,  greatly  detract  from  the 
cogency  of  the  rigorous  mathematical  discussion  carried  through  his 
work  by  Mitscherlich. 

Influence  of  the  several  grain-sizes  on  soil  texture. — Un- 
doubtedly the  most  potent  of  all  the  sediments  appearing  in  the 
above  table  in  influencing  soil  texture,  is  the  "  clay."  That 
the  materials  included  under  this  empirical  designation  may 
vary  considerably  in  different  soils,  has  already  been  sufficiently 
insisted  on;  and  it  is  doubtful  that  in  the  present  imperfect  state 
of  our  knowledge  of  the  functions  of  the  several  physical  grain- 
sizes,  we  would  be  much  wiser  were  we  to  go  to  the  extreme 
advocated  by  Williams  (Forsch.  Agr.  Phys.,  vol.  18,  p.  225,  ff), 
of  determining  with  precision  the  actual  amount  of  such  ex- 
tremely fine  clay  particles  as  cease  altogether  to  obey  the  law 
of  gravity  when  once  suspended  in  water.  It  is  at  least  doubt- 
ful that  the  essential  property  of  adhesive  plasticity  belongs 
only  to  these,  for  this  property  doubtless  increases  gradually 
as  the  size  diminishes,  although  unquestionably  not  a  mere 
function  of  the  latter,  since  it  belongs  only  to  the  hydrated 
silicate  of  alumina. 

Ferric  Hydrate. — Probably  the  body  which  most  commonly  modifies 
materially  the  adhesive  and  contractile  properties  of  the  clay  substance, 
is  ferric  hydrate ;  the  more  as  on  account  of  its  high  density  it  tends 
to  exaggerate  materially,  in  many  cases,  the  apparent  content  of  true 
clay,  and  the  estimate  of  the  soil's  plasticity  based  upon  it.  A  good 
example  in  point  is  the  case  of  soil  No.  246  (Miss.)  of  the  above  table. 
This  is  a  heavy  clay  soil,  yet  not  excessively  adhesive ;  scarcely  as 
much  so  as  No.  230  (Miss.),  the  heavy  gray  "  flatwoods  "  soil,  and 
not  nearly  as  "  sticky"  when  wet  as  No.  173  (Miss.),  the  prairie  sub- 
soil, although  containing  apparently  15  °/0  more  clay  than  the  former, 


PHYSICAL  COMPOSITION  OF  SOILS.  IOi 

and  7  %  more  than  the  latter.  But  No.  246  is  a  highly  ferruginous 
clay,  in  which  the  ferric  hydrate  is  in  a  very  finely  divided  condition, 
and  materially  influences  the  physical  qualities  of  the  clay  substance. 
Were  it  all  accumulated  in  the  "  clay,"  it  would  diminish  the  percen- 
tage of  true  clay  by  11.75%,  reducing  tne  clay-percentage  1028.5% 
which  accords  more  nearly  with  the  soil's  only  moderate  adhesiveness, 
and  not  excessively  heavy  tillage. 

But  it  must  be  remembered  that  the  iron  oxid  shown  in  the 
analysis  is  not  nearly  always  in  this  finely  diffused  condition. 
Frequently  it  incrusts  the  sand  grains ;  quite  commonly  it  forms 
small  concretions  of  limonite,  which  themselves  act  as  sand 
grains;  and  again,  it  may  be  present  in  the  form  of  ''black 
sand  "  or  magnetic  oxid,  as  is  commonly  the  case  in  California 
and  on  the  Pacific  slope  generally.  To  take  this  point  properly 
into  account,  therefore,  it  would  be  necessary  to  determine  the 
amount  of  ferric  hydrate  actually  present  in  the  "  clay  "  as 
separated  by  subsidence  of  the  granular  constituents. 

Other  substances. —  This  circumstance  as  well  as  the  inevi- 
table presence  of  other  modifying  substances,  clearly  shows  the 
desirability  of  being  enabled  to  examine  the  physical  properties 
of  this  "  clay  ''  directly,  by  collecting  its  entire  amount  as  ob- 
tained in  analysis,  instead  of  merely  determining  it  by  weighing 
fractional  portions.  When  this  is  done  the  analysis  is  much 
more  valuable  as  indicating  the  true  tilling  qualities  of  the 
land.  The  increase  of  bulk  suffered  by  this  substance  after 
wetting,  is  a  very  fair  index  of  its  content  of  true  clay,  and  is 
preferable  to  the  chemical  analysis  proposed  by  some  investi- 
gators. For  it  is  quite  impossible  to  distinguish  the  silica  and 
alumina  derived  from  the  kaolinitic  substance  proper,  from  that 
which  is  due  to  the  decomposition  of  zeolites. 

It  is  possible,  however,  to  determine  the  possible  maximum 
of  the  kaolinite  ingredient  by  taking  into  consideration  the 
quantitative  ratio  according  to  which  silica  and  alumina  com- 
bine to  form  it,  viz.,  approximately  46 /f  of  the  former  to  40  of 
the  latter,  the  rest  being  water.  By  using  this  calculation  we 
can  often  demonstrate  clearly  the  presence  in  the  "  clay  "  of 
considerable  amounts  (up  to  33^  )  of  aluminic  hydrate:  since 
no  zeolitic  mass  can  contain  as  much  alumina  as  does  kaolinite. 
Whether  the  aluminic  hydrate  be  in  the  form  of  gibbsite. 


IO2  SOILS. 

bauxite,  disapore,1  or  in  the  gelatinous  state,  the  nature  of  the 
soils  containing  it  proves  that  it  is  totally  destitute  of  plasticity 
and  adhesiveness;  and  this  consideration  will  often  serve  to 
explain  the  fact  that  soils  showing  in  their  chemical  analysis 
high  percentages  of  alumina,  nevertheless  show  quite  low  de- 
grees of  plasticity,  adhesiveness  and  water  absorption.  What 
part  it  may  take  in  modifying  the  physical  properties  of  the 
soil  we  can  thus  far  only  conjecture. 

Influence  of  the  granular  sediments  upon  the  tilling  qualities 
of  Soils. — Considering  the  granular  sediments  by  themselves, 
in  the  absence  of  clay,  it  may  be  stated  in  a  general  way  that 
while  in  a  moist  condition  they  flocculate  sufficiently  to  pro- 
duce a  fair  tilth,  they  will  nevertheless  on  drying  collapse  into 
a  close  arrangement  resulting  from  the  single-grain  structure. 
The  form  of  the  grains  being  angular  instead  of  rounded,  they 
are  apt  to  form  a  very  closely  packed  mass  far  from  suitable 
to  vegetable  growth ;  as  will  be  seen  by  an  example  taken 
from  one  of  the  culture  stations  of  the  University  of  California, 
from  a  piece  of  land  which  on  the  surface  would  be  called  a 
very  sandy  loam,  but  after  we  descend  increases  in  its  content 
of  fine  grains  until  at  a  depth  varying  from  eighteen  inches  to 
three  feet  we  find  w7hat  appears  to  be  a  hardpan,  which  is 
equally  impervious  to  roots  and  water  and  causes  the  water  to 
stagnate  to  such  an  extent  that  after  heavy  rains  the  land 
becomes  so  boggy  as  to  render  plowing  almost  impossible  with- 
out endangering  the  team.  A  close  examination  of  this  hard- 
pan  shows  that,  unlike  others;  it  is  devoid  of  any  cement,  and 
when  taken  out  can  be  readily  crushed  between  the  fingers,  and 
softens  in  water,  but  does  not  become  plastic.  Its  impervious- 
ness  is  therefore  due  solely  to  the  close  packing  of  the  sand 
grains,  for  it  contains  practically  no  plastic  clay,  and  under 
the  microscope  the  grains  are  seen  to  be  angular-wedge-shaped 
and  composed  of  the  remnants  of  granite.  The  physical 
analysis  shows  the  following  result : 

1  Bauxite  is  not  only  the  most  abundant  of  the  three  hydrates  of  alumina 
known  to  occur  naturally,  but  also  stands  nearly  midway  between  the  two  others 
in  its  water  content,  viz.,  a  little  over  25°0;  that  of  diaspore  being  nearly  15°^ 
gibbsite  about  35°  0. 


PHYSICAL  COMPOSITION  OF  SOILS. 


MECHANICAL  ANALYSIS  OF  HARDPAN. 


103 


Designation. 

Diameter. 

Percentage. 

Sand  • 

.50  mm. 
•30 

10.93 
21.23 

Silt  

.16 

.12 

.072 
.047 

.cn6 

7-5* 

7.27 

9-63 

I2.OO 
7.10 

"Clay"  

.02  s 
.016 
;> 

1.25 
I4.2O 
8.64 

It  is  doubtful  whether  this  condition  of  things  can  be 
remedied  by  the  usual  measure  of  breaking  up  the  hardpan 
either  by  hand  or  by  means  of  giant-powder  blasting.  Ex- 
perience seems  to  show  that  the  effect  is  only  temporary,  and 
that  in  the  course  of  time,  by  the  action  of  the  percolating 
waters,  the  particles  settle  back  into  their  original  impervious 
condition.  It  is  just  possible,  however,  that  if  once  penetrated 
by  roots,  the  intervention  of  these  would  permanently  destroy 
the  close  structure,  so  as  to  make  this  a  fair  subsoil  for  the 
growth  of  trees  and  other  plants.  The  writer  is  not  aware  that 
this  kind  of  purely  physical  hardpan  without  cement  has  ever 
been  observed  elsewhere. 

This  physical  condition  is  doubtless  responsible  for  two  other 
phenomena,  viz.,  the  "  putty  soils,"  and  also  certain  difficulties 
experienced  in  irrigation. 

"  Putty  Soils  '"  is  the  name  popularly  given  in  the  Cotton 
States,  and  probably  elsewhere,  to  soils  usually  occurring  in  low 
ground  and  also  known  as  "  cray-fishy."  They  consist  of  very 
uniform,  powdery  sediment,  with  little  or  no  coarse  sand  and 
still  less  of  clay  to  render  them  coherent.  When  wet  these 
soils  behave  precisely  as  would  glazier's  putty,  adhering  to  the 
surface  of  even  the  best-polished  plowshare,  so  that  no  furrow- 
slice  can  be  turned  and  the  plow  is  soon  dragged  out  of  the 
ground.  At  a  very  closely  limited  condition  of  moisture  such 
lands  may  plow  fairly  well ;  but  when  this  limit  is  passed  in 
the  least  (as  sometimes  happens  in  the  course  of  a  single  day), 
it  turns  up  only  hard  clods,  which  in  a  few  hours  of  sunshine 
become  so  hard  that  no  instrument  of  tillage  short  of  a  sledge- 


104 


SOILS. 


hammer  will  make  any  impression  upon  them.  The  physical 
analysis  of  these  usually  gray  soils  shows  that  they  contain  only 
a  trifling  amount  of  clay;  perhaps  i  or  2%,  playing  the  part 
of  linseed  oil  in  making  putty  out  of  whiting.  Even  the  addi- 
tion of  lime  does  not  help  such  soils  much,  because  there  is 
little  or  no  clay  to  flocculate.  They  are,  as  a  matter  of  fact, 
among  the  most  refractory  lands  the  farmer  has  to  deal  with. 
A  soil  showing  similar  behavior,  though  not  quite  as  extreme 
as  in  the  case  of  the  Gulf  or  Cotton  States'  soils  in  question, 
occurs  at  the  culture  substation  at  Paso  Robles,  California, 
and  is  probably  closely  correlated  to  the  physical  hardpan  re- 
ferred to  above.  The  physical  analysis  of  this  soil  yielded  the 
following  result : 


MECHANICAL  ANALYSIS  OF  SOIL. 


Designation. 

Diameter. 

Percentage. 

Sand  \ 

•5°  m 

'32 
.16 

.12 

.072 
.047 
.036 
.025 
.Ol6 
? 

m. 

14.24 

I5-1? 
8.88 
5-6o 
6-75 
8-35 
8.55 
6.03 

'7-77 

7-5° 

Silt  -j 

"Clay"  

It  would  seem  the  best  and  almost  only  remedy  to  be  ap- 
plied to  such  soils  as  these  is  the  introduction  of  vegetable 
matter  or  green-manuring,  by  which  their  texture  is  loosened : 
for  the  hauling  of  mere  clay  upon  the  land  would  hardly  ac- 
complish the  purpose  intended,  within  the  limits  of  farm 
economy. 

Dust  Soils,  which  during  the  dry  season  are  even  in  their 
natural  condition  so  loose  as  to  rise  in  clouds  and  render  travel 
very  uncomfortable,  are  not  uncommon  in  arid  countries,  e.  g., 
in  Washington  and  adjacent  parts  of  Oregon,  on  the  uplands 
bordering  the  Columbia,  Yakima  and  Snake  rivers.  The 
physical  analyses  of  three  of  such  soils,  given  in  the  table  be- 
low, will  convey  some  idea  of  their  peculiarities  in  this  respect. 


PHYSICAL  COMPOSITION  OF  SOILS. 

PHYSICAL  ANALYSIS  OF  DUST  SOILS. 


105 


Hydr.  Value. 

Diameter. 

No  17. 

No.  37. 

No.  79. 

Clay  

*i  0023  mm 

<  10  —  ' 

.Q-J 

-i.ro 

1.27 

Silt  -1 

<.25  mm. 
.25  to       .5 

.010 
.016 

3°-93 
3.20 

J-3J 
13.06 
5.82 

32.29 
12.75 

Sand  

•  5  tO       2.O 

2.0  to     8.0 
8.0  to   64.0 

.025—  .047 
.047.  —  .120 

.12  —    .SO 

7.18 
21.88 

-12.1.Q 

27-37 
43-73 

49-57 

37.51 
10.92 

3-97 

Total  

06.  Z7 

98^18 

98.72" 

Slow  penetration  of  Water. — Soils  of  this  class  are  wetted 
with  extreme  slowness  by  irrigation  water;  so  that  when  first 
taken  under  cultivation  it  sometimes  takes  twenty-four  hours  to 
soak  the  land  for  twelve  inches  in  each  direction.  Irrigation 
furrows  must  be  placed  very  close  together  and  in  large  num- 
bers, in  order  to  ensure  the  wetting  of  the  soil  so  that  the  crop 
shall  not  suffer  from  lack  of  moisture  at  a  distance  of  two  or 
not  more  than  three  feet.  Where  the  irrigation  furrows  are 
drawn  farther  apart  a  fine  stand  of  grain  may  be  seen  within 
eighteen  inches  of  the  same,  while  farther  away  the  crops  may 
be  dying  from  lack  of  moisture.  This  difficulty  is  by  no  means 
infrequent  in  the  arid  region,  and  is  difficult  to  overcome  except 
by  frequent  and  thorough  tillage,  which  gradually  increases  the 
rapidity  of  water-penetration ;  as  has  been  shown  in  the  soils 
of  the  alluvial  prairies  of  the  Yakima  country  in  the  State  of 
Washington.  It  is  necessary,  however,  to  take  care  that  they 
shall  always  contain  an  adequate  amount  of  humus  or  vege- 
table matter,  in  order  to  prevent  re-consolidation  by  the  burn- 
ing-out of  the  humus  during  the  warm,  rainless  season. 

There  is  an  unmistakable  resemblance  between  these  dust 
soils  of  the  Xorthwest  and  the  "  putty  "  soils  mentioned  above; 
both  showing  a  very  low  percentage  of  clay  with  a  relatively 
large  amount  of  the  finest  sediments,  with  a  sudden  downward 
break  of  the  curve  before  the  coarser  grain-si/es  are  reached. 
It  would  seem  as  though  the  absence  of  these  intermediate 
grains  favors  the  close  packing  of  the  fine  sediments  in  the 
interstices  of  the  coarse  ones,  thus  bringing  about  the  imper- 
viousness,  \vhich  is  the  chief  obstacle  to  their  cultivation. 

Effects  of  coarse  Sand. — Coarse  sand  intermingled  with 
heavy  clay  soils  has  but  little  effect  in  improving  the  tilling 
qualities,  unless  carried  to  such  excess  as  renders  it  financially 


106  SOILS. 

impracticable.  In  actual  practice  it  is  frequently  possible  to 
improve  such  soils  by  properly  distributing  upon  them  the 
washings  of  the  adjacent  hills,  which  will  always  carry  sands 
of  many  grades;  and  when  it  is  intended  to  improve  garden 
land  by  hauling  sand  it  is  important  to  choose  the  latter  so  as  to 
complement  the  deficient  grain-sizes  of  the  soil.  The  sand  of 
wind  drifts  or  dunes  is  generally  well  adapted  to  such  improve- 
ment, being,  as  Udden  x  has  shown,  of  a  fairly  definite  com- 
position of  sufficiently  wide  range  of  grain-sizes  for  the  pur- 
pose. 

The  effects  of  humus  in  modifying  soil  texture  are  discussed 
farther  on. 

1  The  Mechanical  Composition  of  Wind  Deposits,  Bull.  No.  i,  Augustana  Library 
Publications;  1898. 


CHAPTER  VII. 

THE  DENSITY   AND  VOLUME-WEIGHT  OF  SOILS. 

ASIDE  from  the  humus-substances  the  specific  gravity  of  the 
common  soil  constituents,  taken  individually,  do  not  vary 
widely;  kaolinite  being  the  lightest  (2.60),  feldspar  next 
(2.62);  then  quartz  (2.65),  calcite  (2.72).  Mica  and  horn- 
blende range  (according  to  their  iron  contents)  from  2.72 
to  over  3.0.  The  average  specific  gravity  of  soils  of  ordinary 
humus  content  only  will  thus  range  between  2.55  and  2.75  ; 
sandy  soils  approaching  very  closely  to  that  of  quartz  alone. 

Volume-Weight. — The  specific  gravity  of  the  soil  is,  how- 
ever, of  little  practical  consequence  compared  with  the  "  volume- 
weight,"  i.  e.,  the  weight  of  the  natural  soil  as  compared  with 
an  equal  bulk  of  water.  A  cubic  foot  of  water  weighs  62^/2 
pounds ;  a  similar  volume  of  soil  usually  weighs  more,  but  in 
the  case  of  peaty  lands  may  actually  (when  dry)  weigh  less. 
The  extreme  range  is  from  no  pounds  for  calcareous,  and 
somewhat  less  for  siliceous  sand,  to  as  little  as  30  to  50  pounds 
in  the  case  of  peaty  and  swamp  soils.  It  may  be  conveniently 
remembered  that  while  average  arable  loams  range  from  80  to 
about  95  pounds  per  cubic  foot,  "  heavy  "  clay  soils  range  from 
75  pounds  down  to  69.  observed  by  the  writer  in  the  case  of 
certain  alluvial  soils,  poor  in  humus,1  of  the  Sacramento  river, 
California.  Manured  garden  soils,  and  the  mold  surface  soil  of 
deciduous  forests,  generally  contain  so  much  humus  as  to 
depress  their  weight  considerably,  varying  according  to  their 
state  of  tilth  from  66  to  70  pounds  per  cubic  foot. 

IV eight  per  acre-foot. — As  for  practical  purposes  and  calcu- 
lations it  is  often  desirable  to  know  approximately  the  weight  in 
pounds  of  an  acre  (43.560  square  feet)  one  foot  deep,  it  is 
convenient  to  remember  that  in  the  case  of  sandy  land,  this 
weight  (per  "acre-foot")  may  be  assumed  at  four  millions 
of  pounds;  for  loams,  at  3'j  millions;  for  clay  lands,  3^.4 

1  This  remarkable  soil  seems  to  have  been  derived  from  the  finest  "slickens  "  of 
the  hydraulic  gold  mines. 

107 


io8 


SOILS. 


millions ;  for  humus  or  garden  land  and  woods  earth,  about  3 
millions  of  pounds;  for  reedy  swamp  and  peaty  lands,  2  to  2*/a 
millions. 

The  loose  tilth  and  humus-content  of  the  surface  soil  will  in  general 
cause  it  to  weigh  less,  bulk  for  bulk,  than  the  underlying  subsoil,  even 
when  the  latter  is  more  clayey ;  moreover,  the  continuous  pressure 
from  above  will  tend  to  consolidate  the  subsoil  and  substrata.  Waring- 
ton  (Phys.  Properties  of  Soils,  pp.  46,  47)  gives  interesting  data  on 
this  point  from  the  Rothamstead  fields,  as  follows : 

Old  pasture,  first  nine  inches 71.3  pounds  per  cub.  ft. 

Same,  fourth  do.     do 102.3       "         "      "      " 

Arable  land,  first      do.     do 89.4       "         "      "      " 

Same,  fourth  do.     do 101.4       "         "      "      " 

The  influence  of  humus  and  unhumified  organic 
matter,  as  well  as  of  tillage,  in  diminishing  the 
volume-weight  of  soils  is  here  strikingly  shown. 


Air-space  in  Natural  Soils. — The  differ- 
ence between  the  specific  gravity  as  usually 
determined,  and  the  volume-weight  of  soils, 
is  of  course  caused  by  the  large  amount  of 
air  contained  in  them  when  dry,  but  which 
in  wetting  them  is  partially  or  wholly  re- 
placed by  water. 

Theoretically,  assuming  all  soil  grains 
to  be  globular,  and  packed  as  closely  as 
possible  (in  oblique  order),  the  space  not 
filled  by  them  would  be  the  same  for  all 
sizes,  whether  that  of  marbles,  or  so  min- 
ute as  to  be  hardly  felt  between  the  fingers ; 
and  would  be  25.95  Per  cent  °f  tne  so^ 
volume.1  If  the  same  globular  particles 
were  packed  as  loosely  as  possible,  i.  c.,  in 
square  instead  of  oblique  order  (see  figures 
10  and  u),  the  vacant  space  would  be 
47.64  per  cent.  If  however  we  imagine 
each  sphere  to  be  itself  composed  of  a  num- 
ber of  smaller  ones,  the  empty  space  will 

FIG.   to.— Various    possible      ....  . 

arrangements  of  soil  particles,  obviously  be  greatly  increased,  to  an  ex- 

1  King,  Physics  of  Agriculture,  p.  116,  ff. 


THE  DENSITY  AND  VOLUME-WEIGHT  OF  SOILS. 


109 


tent  proportionate  to  the  diminution  of  solid  mass  thus  brought 
about.  The  pore-space  might  in  that  case,  with  the  oblique 
arrangement  of  the  globules  as  shown  in  Fig.  10,  be  as  high  as 
74.05  per  cent.  But  since  the  soil  particles  may  be  of  all 
shapes  and  sizes  within  the  same  soil,  and  usually  fit  much 
more  closely  than  would  globular  grains,  the  empty  space  rarely 
approaches  (only  in  certain  alluvial  soils  and  in  loose  mulches) 
to  the  figure  last  named.  In  sandy  soils  it  may  fall  as  low  as 
20%,  and  in  coarse  gravelly  soils  even  as  low  as  10%.  Most 
cultivated  soils  range  between  35  and  $0%  of  empty  space. 

Effects  of  Tillage. — That  these  figures  can  be  only  approxi- 
mations is  obvious  from  the  consideration  that  one  and  the 
same  soil  will  vary  materially  in  its  volume-weight  according 
to  its  temporary  condition  of  greater  or  less  compactness. 
After  land  has  been  beaten  by  winter  rains,  its  volume-weight 
will  be  found  to  have  materially  increased  from  the  well-tilled 
condition  brought  about  by  thorough  cultivation.  This  differ- 
ence is  strikingly  seen  when,  in  plowing,  the  height  of  the 
ground  on  the  land  side  is  compared  with  that  of  the  turned 
furrow-slice  in  well  conditioned  loamy  land.  This  loose  con- 
dition is  called  tilth,  and  it  results  from  the  formation  of 
relatively  large,  complex  crumbs  l  or  floccules,  between  which 
there  are  large  air  spaces  that  were  wholly  absent  in  the  un- 
tilled  land ;  the  floccules  themselves  being  also  more  loosely 
aggregated  than  was  the  case  before  tillage. 

Crumb  or  Flocculated  structure. — Figure  1 1  illustrates  the 
difference  between  the  unplowed  land,  consolidated  especially 
on  the  surface  by  winter  rains,  and  in  its  upper  portion  con- 
sisting largely  of  single  grains ;  while  the  plowed  land,  toward 
which  the  furrow-slices  have  been  turned,  is  greatly  increased 
in  height  and  volume  and  consists  almost  wholly  of  variously- 
shaj>ed  and-sized  aggregates  or  iloccules,  loosely  piled  upon 
one  another  and  separated  by  large  interspaces.  The  increase 

1  The  word  crumbs,  which  is  generally  understood  as  meaning  a  relatively  large, 
loose  aggregate,  seems  preferable  to  the  word  kernels,  suggested  for  the  same  by 
King  (Physics  of  the  Soil,  p.  110).  Kernels  are  understood  to  be  bodies  rather 
more  solid  than  the  surrounding  mass,  and  do  not  convey  the  idea  of  loose  aggre- 
gates. The  word  "  Krumelstructur  "  (crumb-structure),  adopted  by  Wollny  for 
this  phenomenon,  has  both  fitness  and  priority  in  its  favor. 


IIO  SOILS. 

in  volume  from  consolidated  clay  to  crumb-structure  is  given  by 


-wr>n 


1L. 


;  ••-^.«?;;,«i«8>?iL__         Tr"*-^-/ •'''':  '-\;1i>-^:y  -1:$'  !:S^^.>.Va'i';'^.^_'.vj'i'/l 

;y-("";--;'v;:-^          ^~'7^T^V?>. •  >''?T?^- 'T^TT?  {"J^S 

FIG.  n. — Land  before  and  after  plowing.  The  compactness  of  the  soil  is  indicated  by  the  density 
of  dotting.  Before  plowing  there  is  a  compact  surface  crust  (s),  below  which  the  soil  becomes  less 
and  less  compact  as  we  go  deeper.  After  plowing  we  find  the  soil  (fs,  furrow-slice)  converted  into  a 
loose  mass  of  crumbs  (floccules),  with  increase  of  bulk.  Compacted  plow-sole  at  pi 

Wollny  (Forsch.,  vol.  20,  p.  13,  1897)  at  41.9%,  to  powder  as 

33%.  On  moistening  dry  clay 
increased  36.9%,  quartz  powder 
8.01%.  When  land  is  plowed 
in  the  proper  moisture-condition 
the  crumbs  of  floccules  are  held 
together  by  the  surface  tension  of 
the  capillary  films  (menisci)  of 
water  at  the  points  of  contact.  In 
the  case  of  sands,  the  crumbs  will 
collapse  into  single  grains  when- 

F,G.,2.-A  soil-crumb     magnified  to  h       water_films    evaporate,    tin- 

show  the  particles  of  which   it  is  com- 
posed. The  particlesare  held  together  by    less   some  cementing  substance  was 

»hb™hTh™rv«tteirtTharwtue^p7c»   dissolved     or     suspended     in     the 

between  the  particles  represent  air.  Water.         ( See     figure      12).        LitTlC 

carbonate  is  one  of  the  substances  most  commonly  found  per- 
manently cementing  the  floccules ;  hence  the  ready  tillage  of 
most  calcareous  soils,  and  especially  the  loose  texture  of  the 
"  loess  "  of  the  western  United  States,  and  of  Europe  and 
Asia.  In  these  deposits  we  find  sandy  and  silt  aggregates  or 
concretions  ranging  from  ten  or  more  inches  in  length  (loess 
puppets)  to  microscopic  size,  held  together  by  lime  carbonate, 
but  collapsing  into  silt  and  sand  when  the  material  is  treated 
with  acid  so  as  to  dissolve  the  cement.  The  rough  surfaces 
of  these  aggregates,  gripping  into  each  other,  explain  the 
stability  of  the  steep  loess  cliffs  in  the  United  States,  as  well 
as  in  northeastern  China,  as  observed  by  Von  Richthofen  and 
Pumpelly. 

Clay  is  most  frequently  the  substance  which  imparts  at  least 
temporary  stability  to  the  crumbs  and  crumb-structure;  this  is 


THE  DENSITY  AND  VOLUME-WEIGHT  OF  SOILS.        m 

one  of  its  most  important  functions  in  soils,  as  it  serves  to 
maintain  tilth  once  imparted  by  cultivation,  even  after  the  land 
dries  out.  Beating  rains,  and  cultivation  while  too  wet,  will 
in  this  case  of  course  destroy  the  crumbs  and  the  loose  tilth. 

Other  substances  which  greatly  aid  the  maintenance  of  tilth 
are  the  several  humates  (of  lime,  magnesia,  iron),  which  when 
fresh  are  colloidal  (jelly-like)  like  clay  itself,  but  unlike  the 
latter,  when  once  dried  do  not  resume  their  plastic  form  by 
wetting  (Schloesing).  The  crumbs  thus  formed  are  there- 
fore quite  permanent  and  contribute  to  the  looseness  of  soils 
rich  in  humus.  One  part  of  lime  humate  is  said  by  Schloesing 
to  be  equal  in  cementing  power  to  eleven  parts  of  clay. 

Silica,  silicates  and  ferric  hydrate  are  sometimes  found 
cementing  soil  crumbs,  wholly  or  in  part. 

The  importance  of  the  ready  penetration  of  air,  water  and 
roots  thus  rendered  possible  is  obvious;  and  the  question  arises 
how  it  happens  that  wild  plants  are  able  to  do  without  tillage. 

How  Nature  Tills. — When  we  examine  the  undisturbed  soil 
of  woods  or  prairie  in  the  humid  region,  we  will  as  a  rule  find 
the  natural  surface  soil  in  a  very  good  condition  of  tilth ;  the 
obvious  cause  being  the  presence  in  it  of  an  abundant  network 
of  surface  roots  and  rootlets  of  grasses  arid  herbs,  which  in 
connection  with  the  fallen  foliage  prevent  the  beating  and  com- 
pacting of  the  soil  surface ;  which  can  be  seen  to  happen  before 
the  observer's  eyes  whenever  a  heavy  rain  falls  on  a  bare  land 
surface,  however  well  tilled. 

Crusting  of  Soils. — In  some  soils,  especially  of  the  Gulf 
States,  the  beating  of  rain  followed  by  warm  sunshine  so 
effectually  compacts  the  surface  that  in  the  case  of  taprooted 
plants  like  cotton,  it  becomes  necessary  to  cultivate  after  each 
rain,  so  as  to  break  the  crust  that  would  otherwise  not  only 
prevent  the  proper  circulation  of  air.  but  would  also  serve  to 
waste  the  moisture  of  the  land.  The  same  land  in  the  wild 
condition  suffered  no  such  change,  being  protected  by  the 
native  vegetation,  and  by  fallen  leaves.  (See  chapt.  8). 

Soils  of  the  arid  region. — In  the  regions  of  deficient  rain- 
fall the  conditions  are  modified  in  sevcrnl  rcsjx?cts.  Grass 
sward  rarely  exists,  nearly  all  grasses  assuming  the  habit  grow- 
ing in  tufts  or  bunches  some  distance  (a  foot  or  two)  apart; 


H2  SOILS. 

hence  the  name  of  "  bunch  grass  "  commonly  used,  which  how- 
ever means  not  any  one  definite  kind  of  grass,  but  serves  to 
distinguish  the  grasses  of  the  uplands  from  those  of  the  moist 
lowlands,  where  true  sward  may  be  found.  Between  these 
bunches  of  grass  the  soil  is  fully  exposed,  and  being  free  from 
roots  and  leaf-covering  is  compacted,  unless  its  nature  is  such 
that  the  usually  gentle  rains  do  not  produce  a  serious  crusting 
of  the  surface. 

That  such  is  actually  the  predominant  nature  of  the  soils 
formed  under  arid  influences  has  already  been  stated;  and 
thus  the  hard-baked  soil-surface  so  often  seen  in  the  Eastern 
United  States  in  unplowed  bare  land,  or  during  the  prevalence 
of  a  drought,  is  rarely  seen  in  the  arid  region.  The  clay  lands 
that  do  exist  are  usually  sufficiently  calcareous  to  possess  the 
property  of  "  slaking  "  into  crumbs  whenever  wetted  after  dry- 
ing. But  where  this  is  not  the  case,  the  stony  hardness  brought 
about  by  the  long  dry  and  warm  season  is  long  in  being  re- 
moved by  the  winter  rains. 

Charges  of  soil-volume  on  wetting  and  drying. — The  be- 
havior of  colloidal  clay  in  the  above  respects  has  already  been 
described  above  (see  chapt.  4,  page  59).  It  is  obvious  that 
whenever  soils  contain  a  large  proportion  of  such  clay,  their 
behavior  on  wetting  and  drying  will  approximate  to  those  of 
the  pure  clay.  This  is  exemplified  in  the  heavy  clay,  or  so- 
called  "  prairie  soils "  of  the  United  States,  which  when 
thoroughly  wetted  in  spring  will,  during  a  dry  summer,  form 
wide,  gaping  cracks.  These  in  the  long  summers  of  the  arid 
region  may  extend  to  the  depth  of  several  feet,  with  a  width  of 
as  much  as  three  and  more  inches  at  the  surface  of  the  ground. 
This,  of  course,  contributes  greatly  to  the  drying-out  of  the 
soil  to  the  same  depth,  and  results  as  well  in  the  mechanical 
tearing  of  the  root-system  of  growing  plants;  sometimes 
causing  the  total  destruction  of  vegetation.  In  some  clay  soils 
it  happens  that  after  a  rain  or  irrigation,  the  shrinkage  occur- 
ring upon  the  advent  of  warm  sunshine  will  cause  the  surface 
crust  to  so  contract  around  the  stem,  c.  g.,  of  grain,  as  to  con- 
strict and  injure  the  bark,  causing  serious  injury  to  the  crop. 
In  soils  of  this  character  very  thorough  tillage  in  preparing 
for  a  crop,  and  the  maintenance  of  a  loose  surface  during  its 
growth,  are  of  course  extremely  essential. 


THE  DENSITY  AND  VOLUME-WEIGHT  OF  SOILS.        113 

In  the  arid  region  it  will  frequently  happen  that  such  soils 
when  not  tilled  to  a  sufficient  depth,  will  during  the  later  part 
of  the  summer  so  shrink  and  crack  beneath  the  shallow-tilled 
surface  layer  that  the  latter  will  bodily  fall  into  the  cracks,  ex- 
posing the  roots  to  all  the  deleterious  influences  of  mechanical 
lesion  and  drying-out.  It  is  thus  obvious  that  the  cultivation 
of  such  soils  should  not  be  undertaken  at  all  by  those  not  nat- 
urally able  and  willing  to  bestow  upon  them,  to  the  fullest  ex- 
tent, the  deep  and  thorough  tillage  which  is  absolutely  essential 
in  the  utilization  of  their  usually  high  productive  power. 

Extent  of  Shrinkage. — The  extent  of  this  shrinkage  in  drying,  and 
subsequent  expansion  in  wetting,  have  been  measured  by  the  writer  by 
the  use  of  the  sieve  cylinder  described  below  (chapt.  n,  p.  209),  a^ 
serving  for  the  determination  of  the  water  capacity  of  soils.  When  a 
soil  of  the  kind  above  referred  to  is  placed  in  the  sieve  cylinder  in  the 
tilled  (flocculated)  condition,  then  allowed  to  absorb  its  maximum  of 
water  and  then  dried  at  100  degrees  C.,  the  contraction  in  drying  can 
be  very  strikingly  seen,  and  its  amount  measured  by  filling  up  the 
empty  space  with  mercury ;  then  measuring  the  latter  after  expelling 
the  surplus  by  means  of  a  ground  glass  plate  laid  on  top.  The  con- 
traction of  several  heavy  clay  soils,  thus  measured,  has  been  found  by 
the  writer  to  range  from  28  to  as  much  as  40  per  cent,  of  the  original 
bulk.1  The  soil  thus  contracted,  when  again  wetted,  does  not  return 
altogether  to  its  original  bulk,  but  remains  in  a  more  or  less  compacted 
condition,  like  that  of  a  soil  which  has  been  rained  upon. 

The  expansion  and  contraction  of  a  heavy  clay  soil  on  wet- 
ting and  drying  are  well  illustrated  in  the  figure  below,  in  which 
the  soils  are  shown  in  the  shallow  cylinder  which  serves  for  the 
determination  o'f  water-holding  power  (see  chapt.  i  i,  p.  jo<)). 
The  middle  figure  shows  in  profile  the  expansion  of  a  dry, 
pulverixed  "  black  adobe."  struck  level,  when  allowed  to  absorb 
its  maximum  of  water;  it  rises  above  the  rim  of  the  sieve-box 
to  nearly  the  half  height  of  the  latter.  The  outside  figure  to 
the  right  shows  the  same  soil  after  drying;  that  to  the  left,  a 
red  clay  soil  similarly  treated.  It  is  easily  seen  that  the<r 
variations  in  volume  may  bring  about  very  marked  results  in 

1  Wollny  '  Korsch.  Vol.  20,  p.  13  ff,  1897)  records  similarly  high  shrinkages  in 
his  experiments. 

8 


SOILS. 


the  fields;  the  surface  of  which,  apart  from  the  cracks  usually 
formed,  may  be  several  inches  lower  in  the  dry  season  than 
during  wet  weather. 


, 


RED  CLAY  SOIL.  BLACK  "  ADOHE  "  CLAY  SOIL. 

FIG.  13. — Expansion  on  Wetting  and  Contraction  on  Drying  ol  heavy  clay  soi!s. 

Contraction  on  Wetting. — In  the  case  of  alkali  soils  contain- 
ing much  carbonate  of  soda,  a  very  notable  contraction  occurs 
in  wetting  the  loose,  dry  soil.  The  cause  is  here  obviously  the 
collapse  of  the  crumbs,  formed  in  dry  tillage  or  crushing,  into 
single  grains,  closely  packed.  The  same  result  is  observed  in 
the  naturally  depressed  "alkali  spots"  (see  chapt.  22). 

"  Hog-wallows." — In  the  field  the  wetting  of  cracked  clay 
soils  produces  some  very  curious  effects.  The  effect  of  the 
first  light  rains  usually  is  to  crumble  off  the  edges  or  angles 
near  the  surface,  the  materials  thus  loosened  falling  into  the 
lower  portion  of  the  cracks.  This  is  repeated  at  each  success- 
ive shower  followed  by  sunshine,  the  crevices  thus  becoming 
partly  filled  with  surface  soil.  When,  subsequently,  the  heavier 
and  more  continuous  rains  wet  the  land  fully,  also  causing  the 
consolidated  mass  in  the  crevices  to  expand,  the  latter  cannot- 
cl6se  on  account  of  the  surplus  material  having  fallen  into 
them;  the  result  being  that  the  intermediate  portions  of  the  soil 
are  compelled  to  bulge  upward,  sometimes  for  six  or  more 
inches,  creating  a  very  uneven,  humpy  surface,  well-known  in 
the  southwestern  United  States  as  "  hog-wallows,"  1 

1  A  totally  different  kind  of  "hog-wallows,"'  occurring  in  California  and  the  arid 
region  generally,  have  been  described  in  a  previous  chapter  under  the  head  of 
Aeolian  soils  (See  chapt.  i,  p.  9''. 


THE  DENSITY  AND  VOLUME-WEIGHT  OF  SOILS. 


II 


Such  a  surface  is  always  therefore  an  indication  of  an  ex- 
tremely heavy  soil,  difficult  to  cultivate;  yet  embracing  some 
of  the  most  highly  and  permanently  productive  lands  known  in 
the  United  States,  and  in  India,  where  the  "  regur  "  lands  of 
the  Deccan  are  of  this  character;  they  have  been  cultivated 
without  fertilization  for  thousands  of  years.  The  subjoined 
physical  analyses  of  lands  of  such  extreme  character  as  to  be 
almost  uncultivatable  will  serve  to  exemplify  their  physical 
composition. 

PHYSICAL  ANALYSES  OF  HEAVIEST  CLAY  SOILS. 


No  242  Miss.   No.  643  Cal. 


I  log-wallows 

soil. 

Jasper  Co. 
Mississippi. 


Black  Adobe. 
Contra  Costa 

Co. 
California. 


Weight  of  gravel  over  1.2  mm.  diameter 
"  "  between  1.2  and  i  mm 

"  "  between  i  and  0.6  mm 

Fine  earth  


•83 
i. ig 
_97-9l 

IOO.OO 


FINE  EARTH. 


I 

lydr.  Value. 

Diameter. 

Clay  

<.oo23  mm  
[  -^0.25  mm  

.010 

48.00 

45-96 

0.25  mm  

.016 

T  ^.  I  O 

JJ 

37-64 

Silt                  •{ 

0.5  mm  

.025 

5.50 

2.74 

r  .0  m  m  
2.0  mm  

.036 

.047 

3-74 
2.S4 

3-3' 

2.9s 

4.0  mm  

.072 

.20 

2-^9 

S.o  mm  
1  6.0  mm           

.120 

•27 
oo 

1.68 

•  70 

Sand  

I  f>-r 

->  th 

t  64.0  mm..  .        

•5° 

I.OJ 

2.OO 

—3° 

100.00 

IOO.OO 

It  will  be  noted  that  in  both  these  extremely  heavy  soils  the  sum  of 
the  clay  and  finest  sediments  is  a  little  over  83%. 

It  should  be  stated  that  both  these  soils  after  being  thoroughly 
wetted  become  so  adhesive  that  it  is  almost  impossible  to  travel 
over  the  tracts  occupied  by  them,  and  that  they  are  practically 
almost  untillable,  being  too  adhesive  when  wet;  yet  if  allowed 
to  dry  to  a  certain  extent  ( varying  within  very  narrow 
limits)  they  turn  up  by  the  plow  in  large  clods,  which  after  a 


Il6  SOILS. 

few  hours  of  sunshine  become  of  stony  hardness  and  will  resist 
all  efforts  at  pulverization  or  the  production  of  tilth.1 

Calcareous  Clay  Soils  crumble  on  drying. — The  heavy  clay 
soils  of  some  of  the  calcareous  prairies  of  the  Southwest,  in- 
stead of  contracting  into  a  stony  mass  on  drying,  on  the  con- 
trary resolve  into  a  mass  of  crumbs,  thus  producing  excellent 
tilth.  This  occurs  even  though  the  land  may  have  been 
plowed  when  wet,  and  of  course  is  a  great  advantage.  The 
most  striking  exemplification  of  this  peculiarity  occurs  in  the 
heavy  but  profusely  fertile  "  buckshot "  clay  lands  of  the 
Yazoo  bottom,  in  Mississippi,  where  it  is  usual  to  plant  corn 
and  sweet  potatoes  in  the  semi-fluid  mud  left  after  an  over- 
flow, after  turning  a  shallow  furrow,  then  covering  by  turn- 
ing another.  To  the  onlooker  it  seems  impossible  that  such 
plantings  could  be  successful ;  but  within  a  short  time  the 
muddy  surface  becomes  a  bed  of  crumbs  ("buckshot"), 
forming  a  seedbed  not  readily  excelled  by  any  made  by  arti- 
ficial means.  Hence,  largely,  the  almost  invariable  success  of 
crops  in  the  Yazoo  region. 

Port  Hudson  Bluff. — The  same  clay  produces  a  most  un- 
pleasant result  at  the  foot  of  the  Port  Hudson  bluff,  where  it 
crops  out  some  feet  above  low  water.  When  after  a  freshet  the 
water  level  falls  below  this  stratum,  on  drying  the  clay  dis- 
integrates into  crumbs  just  as  does  the  Yazoo  buckshot  soil ; 
with  the  result  that  at  the  next  rise,  the  loose  mass  subsides  into 
the  river  as  a  flood  of  mud.  Thus  the  foot  of  the  bluff  is 
being  constantly  undermined,  and  the  falling  of  the  bluff  scarp 
has  obliged  the  town  above  to  recede  many  hundreds  of  feet 
from  its  original  historic  site. 

The  exact  proportions  of  lime  carbonate  necessary  to  produce 
this  phenomenon,  and  its  necessary  relations  to  clay  substance 
and  other  physical  soil  ingredients,  yet  remain  to  be  investi- 
gated.2 

1  In  driving  a  light  carriage  over  the  land  represented  by  No.  643  above,  after  a 
light  rain,  the   wheels   gathered  up   so  much   soil   within  a   hundred  yards  as   to 
render  it  necessary  to  stop  and  chop  it  off  the  tires  by  means  of  a  hatchet.     This 
is  a  common  experience  in  the  black  prairie  lands  of  Texas. 

2  Schiibler    (Grands'atze  d.Agrikulturchemie,    1838)  ascribes  the   crumbling   of 
calcareous  clay  soils  to  the  difference  in    the   contraction    of  calcareous  sand  and 
the  clay  substance.     But   it    is  doubtless  more  directly  connected  with  the  floc- 
culation  of  the  latter  by  lime. 


THE  DENSITY  AND  VOLUME-WEIGHT  OF  SOILS. 


117 


Loamy  and  Sandy  Soils. — It  is  largely  the  absence  of  these 
extreme  changes  of  volume  that  renders  the  cultivation  of 
loamy  or  even  sandy  lands  so  much  more  easy,  and  the  success 
of  crops  so  much  more  safe,  than  is  the  case  in  clay  soils. 
Whenever  the  content  of  colloidal  clay  diminishes  below  15%, 
the  shrinkage  in  drying  from  the  \vet  condition  becomes  so 
slight  as  to  cause  no  inconvenience ;  while  in  sandy  soils  prop- 
erly speaking,  no  perceptible  change  in  volume  occurs. 

Peaty  soils,  however,  and  all  those  containing  a  relatively 
large  amount  of  humus,  are  also  liable  to  visible  shrinkage 
when  passing  from  the  wet  to  the  dry  condition.  But  on  ac- 
count of  their  looseness  and  porosity  such  shrinkage  does  not 
usually  result  in  the  formation  of  cracks  or  rupture  of  the 
roots,  as  is  the  case  in  heavy  clay  lands.  The  entire  mass  of 
the  soil  then  shrinks  downwards,  but  rarely  forms  cracks  on  the 
surface.  Hence  the  introduction  of  humus  into  "  heavy  "  soils 
is  among  the  best  means  of  improving  their  tilling  qualities. 

Formation  of  Surface  Crusts. — Some  soils,  especially  those 
of  a  clay-loam  character,  are  very  liable  to  the  formation  of 
hard  surface  crusts  from  the  beating  of  rains,  and  from  sur- 
face irrigation ;  owing,  doubtless,  to  the  ready  deflocculation 
of  their  clay  substance.  It  is  not  easy  to  define  the  precise 
physical  composition  conducive  to  this  crust  formation;  but 
the  subjoined  physical  analyses  show  examples  of  soils  in 
which  this  tendency  is  very  prominent  and  is  frequently  an- 
noying, in  that  when  they  occur  in  the  regions  of  frequent 
summer  rains,  it  becomes  necessary  after  each  one  to  till  the 
surface  in  hoed  crops  (V.  g.,  in  cotton-fields)  in  order  to  pre- 
vent the  injurious  effects  of  such  consolidation  of  the  surface. 
It  may,  of  course,  be  prevented  by  mulching,  or  on  the  large 
scale  by  green-manuring,  to  such  extent  as  to  prevent  con- 
traction. 

The  subjoined  physical  analyses  of  two  soils  from  the  Brown-I-oam 
region  of  Northern  Mississippi  (see  chap.  24),  shows  the  composi- 
tion of  lands  excellent  in  every  respect  other  than  the  tendency  to 
crust  after  each  rain  : 


u8 


SOILS. 

PHYSICAL  ANALYSES  OF  CRUST-FORMING  SOILS. 


Diameter. 

Hydr.   Value. 

No.  219. 

No.  197. 

Coarse  materials  

I  —  3  mm. 

) 

Sand  ,  -{ 

.5—1   " 

•5° 
.10 

64  mm. 

T.2 

1          '23 

1.47 

2.11 

.70 

Silt  \ 

:?? 

.12 

.072 
.047 

.cn6 

16 

8 
4 

2 
I 

1.17 

.78 
.76 

9-79 

7.  2O 

.18 
.78 
3-56 

1  1  I  2 

Clay  

.025 
.016 
.010 

? 

-50 
•25 
^•25 
<.OO'>1 

I3.n 

*S-°7 
26.36 

JQ  IO 

16.64 

27.28 
18.87 
17  21 

These  soils  agree  in  having  a  sufficient  amount  of  clay  (17  to  19  °/0) 
to  characterize  them  as  clayey  loams,  associated  with  a  very  large  pro- 
portion of  the  grain-sizes  of  less  than  .025  mm.,  or  .5  mm.  hydraulic 
value.  A  higher  proportion  of  clay,  even  though  associated  with  a 
similarly  high  or  even  larger  proportion  of  these  fine  sediments,  seems 
to  prevent  crusting,  probably  because  the  swelling  of  the  clayey  ingre- 
dient on  wetting  and  its  extravagant  contraction  in  drying  breaks  up 
the  continuity  of  the  surface.  The  heaviest  clay  soils,  such  as  those 
shown  on  a  preceding  page,  neither  crust  nor  crumble  on  drying  after 
wetting,  but  contract  into  lumps  of  stony  hardness,  as  a  whole. 

The  burning-out  of  the  humus  from  well-tilled  surface  soils 
during  the  extended  heat  and  dryness  of  rainless  summers, 
brings  about  such  a  contraction  or  packing  of  the  surface  soil 
of  orchards  in  California  as  to  greatly  reduce  their  productive- 
ness, and  to  render  necessary  diligent  green-manuring  as  the 
only  practical  remedy.  In  many  cases,  liming  of  the  surface 
also  serves  well  to  prevent  this  injurious  effect,  which  to  some 
extent  of  course  follows  surface  irrigation  as  well  as  rains. 

In  most  soils,  repeated  alternate  wetting  and  drying  in  place 
produces  a  loose,  flocculated  texture,  so  long  as  no  clefloccula- 
tion  is  brought  about  by  mechanical  causes,  such  as  beating 
rains  or  running  water. 

Effects  of  Frost  on  the  Soil. — The  expansion  suffered  by 
water  in  freezing  necessarily  tends  to  separate  the  soil  par- 
ticles previously  held  together  by  the  surface  tension  of  the 


THE  DENSITY  AND  VOLUME-WEIGHT  OF  SOILS,         ug 

capillary  water,  or  otherwise  flocculated  or  cemented.  Freez- 
ing of  the  soil  is  therefore  of  material  assistance  in  disintegrat- 
ing cloddy,  ill-conditioned  soils,  leaving  them  in  loose,  crumbly 
condition  after  the  ice  has  melted  and  the  surplus  water  drained 
off;  so  as  to  materially  facilitate  tillage  and  root  penetration. 
When,  however,  soils  thus  circumstanced  are  tilled  or  trodden 
while  too  wet,  they  quickly  become  puddled,  being  practically 
reduced  to  single-grain  structure.  (See  this  chapt.  p.  no). 
Hence  the  injury  caused  by  allowing  cattle  to  range  in  winter 
on  cultivated  land  subject  to  freezing  and  thawing,  which  it 
sometimes  takes  years  to  correct. 

A  disagreeable  effect  often  produced  by  the  freezing  and 
thawing  of  wet  lands  is  the  "  heaving-cut  "  of  grain,  result- 
ing from  the  upward  expansion  of  the  surface  soil  in  freezing, 
that  may  readily  rupture  the  roots ;  while  on  thawing,  the  soil 
surrounding  the  upheaved  stool  is  apt  to  settle  down,  especially 
in  case  of  a  rain,  leaving  the  stool  and  roots  exposed  either  to 
drying  or  freezing,  as  the  case  may  be.  Hence  the  desire  of 
grain  farmers  in  northern  climates,  for  a  sufficient  covering  of 
snow  to  protect  the  fall-sown  grain,  rather  than  an  ''  open 
winter,"  during  which  the  grain  is  exposed  to  alternate  freezes 
and  thaws,  or  extreme  cold. 

In  certain  soils,  notably  in  those  liable  to  crusting  (p.  117), 
instead  of  heaving  the  soil,  the  water  in  freezing  emerges  bodily 
from  small  cracks,  in  foliated  or  wire-like  forms  ("ice- 
flowers")  resembling  those  of  native  silver,  and  formed  sub- 
stantially in  the  same  way,  by  a  kind  of  "  wire-drawing  "  pro- 
cess, aided  by  crystallization. 

Small  ice-crystals  formed  on  the  surface  of  small  crevices  filled  with 
water  cause  others  to  be  formed  at  their  lower  ends,  and  the  expansion 
occurring  in  freezing,  forces  the  ice  upward  ;  the  process  repeating 
itself  under  favorable  conditions,  until  the  stalks  or  sheets  of  ribbed  ice 
grow  to  a  height  of  several  inches.  This  phenomenon  is  especially 
frequent  in  the  middle  cotton  States — -Arkansas,  Tennessee,  northern 
Mississippi,  etc.,  where  frequent  changes  from  rainstorms  or  thaws  to 
cold  northwest  winds  occur  in  winter. 


CHAPTER  VIII. 

SOIL  AND  SUBSOIL. 
CAUSES  AND  PROCESS  OF  DIFFERENTIATION.     HUMUS. 

Soil  and  Subsoil  Ill-defined. — While  the  general  mass  of  rock 
debris  formed  by  the  action  of  the  agencies  heretofore  dis- 
cussed as  soil-material,  may  under  proper  conditions  be- 
come soil  capable  of  supporting  useful  plant  growth,  universal 
experience  has  long  ago  recognized  and  established  the  dis- 
tinction between  soil  and  subsoil :  by  which  are  ordinarily 
meant,  respectively,  the  portion  of  the  soil-material  usually 
subjected  to  tillage,  and  what  lies  beneath.  There  can  be  no 
question  about  the  practical  importance  of  this  distinction ;  but 
the  definition  of  the  two  terms,  as  commonly  given  in  some 
works  of  agriculture,  is  both  incomplete  and,  in  its  application 
to  many  cases,  partly  misleading. 

The  differentiation  of  soil  and  subsoil  is  due  partly  to  the 
action  of  organic  matter  and  micro-organisms,  partly  to 
physico-chemical  causes,  now  to  be  discussed  in  detail. 

THE  ORGANIC  AND    ORGANIZED   CONSTITUENTS  OF   SOILS. 

Humus  in  the  Surface  soil. — The  most  obvious  mark  of  dis- 
tinction between  soil  and  subsoil  is,  usually,  the  darker  tint 
of  the  former,  due  to  the  presence  of  humus  or  vegetable  mold, 
which  becomes  most  apparent  by  darkening  of  the  tint  when 
the  soil  is  moistened.  Thus  soils  having  a  gray  tint  when  dry, 
may  become  almost  black  when  wetted.  When  no  such  deepen- 
ing of  color  occurs  in  wetting,  the  absence  or  great  deficiency 
of  humus  may  safely  be  inferred.  The  only  other  substance 
whose  presence  may  invalidate  the  conclusions  based  upon  the 
darkening  of  the  soil  tint,  is  ferric  hydrate  (iron  rust),  which 
itself  possesses  the  property  of  darkening  on  wetting,  and  may 
effectually  cover  either  the  presence  or  the  absence  of  humus. 

Since  the  formation  of  the  humus  depends  upon  the  decom- 

120 


SOIL  AND  SUBSOIL.  121 

position  of  organic  matter  (mostly  of  the  cellulose  group) 
derived  partly  from  the  roots,  partly  from  the  leaves  and 
stems  of  plants  growing  and  dying  on  the  soil,  its  accumulation 
near  the  surface  is  natural.  But  since  the  depth  to  which  roots 
penetrate  varies  greatly  not  only  with  different  plants,  but  very 
essentially  in  conformity  with  the  greater  or  less  penetrability 
of  the  soil  and  susoil,  the  depth  to  which  the  dark  humus  tint 
may  reach  vertically  varies  correspondingly,  from  two  or  three 
inches  to  several  feet.  In  the  case  of  soils  that  have  been 
formed  by  the  gradual  filling-up  of  swamps  or  marshes,  the 
humus-tint  may  reach  to  several  yards  depth. 

Surface  Soil,  and  Subsoil. — It  is  thus  apparent  that  the  term 
"  surface  soil,"  while  commonly  confined  by  the  farmer  to  the 
portion  turned  by  the  plow  or  usually  reached  in  cultivation  by 
any  implements,  may  or  may  not  belong,  functionally,  to  layers 
of  greatly  varying  thickness.  Similarly  the  term  subsoil  may 
or  may  not  refer,  in  individual  cases,  to  parts  of  the  soil  mass 
materially  different  from  the  surface  soil.  Yet  this  distinction 
is  of  no  mean  practical  importance,  because  the  efficacy  of  one 
of  the  most  common  measures  of  soil  improvement,  viz.,  sub- 
soil plowing  or  "  subsoiling,"  depends  materially  upon  the 
differences  between  soil  and  subsoil  in  each  particular  case. 
Most  of  the  diversity  of  opinion  regarding  the  merits  of  this 
operation  is  simply  the  result  of  a  corresponding  diversity  in 
the  natural  facts  and  cultural  practice  of  each  case. 

Causes  of  the  Differentiation  of  Soil  and  Subsoil. — One  of 
the  prominent  points  of  difference  between  surface  soils  and 
subsoils  has  already  been  mentioned  in  the  usual  predominance 
of  root-mass  in  the  upper  layers;  to  which  is  added  a  part  at 
least  of  the  substance  of  fallen  leaves  and  stems  of  its  vegeta- 
tion. How  much  of  this  vegetable  mass  ultimately  becomes 
converted  into  humus,  as  well  as  the  nature  of  the  product 
formed,  depends  upon  a  great  variety  of  circumstances;  some 
of  which  have  already  been  mentioned  in  connection  with  the 
general  discussion  of  humification  ( chapt.  2,  p.  20).  Briefly 
stated,  the  main  controlling  conditions  are:  the  amount  of 
water  or  moisture  present,  the  access  of  air  (  oxygen),  a  proper 
temperature,  and  the  presence  of  the  several  organisms  which 
in  the  course  of  time  take  part  in  the  process  of  soil-formation. 


122  SOILS. 

Ulmin  Substances;  Sour  Humus  (Germ.  Rohhumus). — In 
the  presence  of  so  much  moisture  or  liquid  water  as  will  mater- 
ially impede  the  access  of  air,  and  with  the  concurrence  of 
reasonably  low  temperatures,  the  organisms  that  at  first  take 
the  chief  role  in  the  transformation  of  the  vegetable  tissues  into 
humus-like  substances  are  bacteria.  But  the  antiseptic  nature 
of  the  compounds  thus  formed  1  soon  puts  an  end  to  their  ac- 
tivity, and  thereafter  the  process  seems  to  be  a  purely  chemical 
one,  and  very  slow.  In  peat  bogs,  the  transition  from  the  fresh, 
dead  stems  and  roots  to  brown  peat  is  easily  followed  down- 
ward, white  cellulose  fibers  remaining  apparently  unchanged 
to  some  depth ;  so  that  such  fiber  has  been  used  for  tissues  and 
paper.  The  solid  decomposition-products  are  brown  substances, 
partly  soluble  in  water  and  imparting  to  it  a  brown  or  coffee 
color  (frequently  seen  in  the  drains  of  marshes)  and  an  acid 
reaction;  the  latter  due  to  ulmic  (as  well  as  apocrenic)  acid, 
readily  soluble  in  caustic  and  carbonated  alkalies,  and  forming 
insoluble  salts  with  the  earths  and  metals;  while  another  por- 
tion, ulmin,  is  insoluble  in  the  same,  but  gradually  becomes 
soluble  by  oxidation. 

The  gaseous  products  formed  under  these  conditions  are 
carbonic  dioxid  and  "marsh  gas"  (methan,  CH4),  the 
former  predominating  in  the  early  stages;  while  later,  the  car- 
buretted  hydrogen  predominates,  rendering  the  gas  readily  in- 
flammable. 

Sour  Soils. — The  "  sour  "  soils  thus  produced  in  nature  in 
presence  of  excess  of  water  bear  only  "  sour  "  growth,  such 
as  sedges  and  rushes,  of  little  agricultural  value;  they  usually 
require  reclamation  processes  before  becoming  adapted  to  ordi- 
nary crops.  In  old  forests  of  northern  climates  a  peaty  and 
more  or  less  acid  layer  is  sometimes  formed  on  the  surface, 
above  the  black  woods-earth,  and  retards  somewhat  the  full 
production  of  such  land  when  taken  into  cultivation.2 

Marshes  and  swamps,  both  fresh  and  salt,  as  above  stated 
usually  show  coffee-colored  waters,  which  are  also  characteristic 
of  the  streams  that  drain  them,  until  by  intermixture  with 

1  The  antiseptic  properties  of  sour  humus  are  well  exemplified  in  the  perfect 
state  of  preservation  in  which  the  remains  of  animals,  wood  implements,  etc.,  are 
found  in  bogs  into  which  they  have  sunk  in  prehistoric  times. 

2  See  Muller,  Natiirliche  Humusformen. 


SOIL  AND  SUBSOIL. 


I23 


waters  containing  lime  salts,  the  ulmic  substances  are  neutral- 
ized and  precipitated.  Such  neutralization,  preferably  by 
means  of  lime,  is  the  first  step  towards  the  reclamation  of  lands 
bearing  "  sour  "  vegetation.  The  acid  reaction  characterizing 
the  ulmic  substances  is  also  characteristic  of  many  woodlands, 
notably  in  the  United  States  of  the  soils  of  the  ''  Long-leaf- 
pine  "  region  of  the  Cotton  States,  both  upland  and  lowland, 
as  well  as  of  many  deciduous  forests  in  northern  climates. 
Hence  liming,  whether  artificial  or  natural,  effects  a  most  not- 
able improvement,  together  with  a  marked  change  of  vegeta- 
tion, in  these  lands. 

It  has  been  long  known  that  after  long-continued  cultivation,  soils 
originally  of  neutral  or  slightly  basic  reaction  become  acid  :  and  the 
liming  of  such  lands  is  an  ancient  practice  in  Europe.  The  matter, 
however,  received  but  scant  attention  until  Wheeler  and  Hartwell,  of 
the  Rhode  Island  Experiment  Station,  demonstrated  the  almost  univer- 
sal acid  condition  of  the  older  lands  of  that  State,  and  the  excellent 
effects  produced  by  neutralization  with  lime,  or  even  with  the  alkali 
carbonates.1  The  current  neutralization  of  the  humus-acids  is  unques- 
tionably one  of  the  cardinal  advantages  of  calcareous  lands ;  for  such  as 
contain  only  small  amounts  of  lime  carbonate  will  of  course  become  acid 
more  quickly  under  cultivation. 

IJumin  Substances. — In  the  presence  of  only  a  moderate 
amount  of  moisture,  therefore  under  the  influence  of  a  more  or 
less  rapid  circulation  of  air,  and  in  the  presence  of  earthy 
carbonates  (especially  that  of  lime)  to  prevent  the  formation 
of  acids,  or  to  neutralize  them  as  formed,  the  normal  process 
of  humification  occurs;  mainly  under  the  influence  of  fungous 
instead  of  bacterial  growths.  The  various  molds  take  a 
prominent  part  in  the  conversion  of  the  vegetable  substance 
into  black,  neutral,  insoluble  humus  compounds.  Such  fungous 
vegetation  is  always  accompanied  by  the  evolution  of  carbonic 
gas.  and  the  resulting  fungous  tissues  are  markedly  richer  in 
nitrogen  and  carbon  than  the  substance  of  the  higher  plants 
from  which  they  were  derived  (see  chapt.  9).  Com- 
parative analyses  show  that  in  the  normal  process  of  humifica- 
tion of  vegetable  substances,  oxygen  and  hydrogen  are  climi- 

1  Reports  of  the  Rhode  Island  Exp't  Station,  1895.  and  ff. 


I24 


SOILS. 


nated  in  the  form  of  water  and  carbonic  dioxid,  while  at  the 
same  time  there  is  an  increase  in  the  percentage  of  carbon,  and 
generally  also  of  nitrogen ;  the  latter  more  particularly  in  the 
case  of  vegetable  matter  not  very  rich  in  that  element.  When 
once  humification  is  complete,  oxidation,  especially  under  arid 
conditions,  bears  mainly  upon  the  carbon  and  hydrogen,  so 
that  the  nitrogen  content  may  rise  to  very  high  figures ;  while 
another  portion  is  ultimately  wholly  oxidized,  with  the  forma- 
tion of  nitrates,  under  the  influence  of  the  nitrifying  bacteria, 
this  being  the  process  chiefly  efficient  in  the  nutrition  of  vegeta- 
tion with  nitrogen. 

As  a  matter  of  course,  the  several  organic  compounds  contained  in 
plants  may  continue  to  exist  in  soils  for  some  time,  varying  according 
to  conditions  of  temperature  and  moisture.  Thus  dextrin,  glucose,  and 
even  lecithin  and  nuclein  have  been  reported  to  be  found.  The  activity 
of  the  numerous  fungous  and  bacterial  ferments  under  favoring  condi- 
tions will,  of  course,  limit  the  continued  existence  of  such  compounds 
somewhat  narrowly,  so  that  they  can  hardly  be  considered  as  active  soil 
ingredients  save  in  so  far  as  they  favor  the  development  of  the  bacterial 
flora. 

Porosity  of  Humus. — One  of  the  essential  features  of  na- 
tural humus  is  its  great  porosity,  whereby  it  not  only  becomes 
highly  absorbent  of  water  and  gases,  but  is  also  gradually  oxi- 
dized, probably  under  the  influence  of  bacteria.  For  this  oxi- 
dation, as  measured  by  the  evolution  of  carbonic  gas,  pro- 
gresses most  rapidly  under  the  same  conditions  as  to  moisture, 
temperature  and  access  of  air,  that  are  known  to  be  most  favor- 
able to  fungous  and  bacterial  growth.  Hence  the  formation  of 
carbonic  dioxicl  in  the  soil  is  assumed  to  be  the  measure  of  the 
intensity  of  such  activity. 

Physical  and  Chemical  Nature  of  the  Humus  Substances. — 
The  humus  substances  are  gelatinous  when  moist,  but  are 
neither  markedly  adhesive  or  plastic.  Like  the  other  colloidal 
substances  of  the  soil,  they  serve  to  retain  both  gases  and 
vapors,  including  moisture,  liquid  water,  and  its  dissolved 
solids.  In  the  natural,  porous  condition  they  are  powerfully 
absorbent  of  gases,  including  especially  aqueous  vapor.  Dry 
humus  swells  up  visibly  when  wetted,  the  volume-weight  in- 


SOIL  AND  SUBSOIL.  125 

creasing  to  the  extent  of  two  to  eight  times  ;  so  that  humus 
stands  foremost  in  this  respect  among  the  soil  constituents. 
The  density  of  natural  humus  is  about  1.4,  being  the  lightest 
of  the  soil  constituents.  Hence  soils  rich  in  humus  are  *'  light  " 
not  only  in  the  farmer's  sense  of  being  easily  tilled  when  not 
too  wet,  but  also  of  light  weight  for  equal  volumes  when  com- 
pared with  clayey  and  sandy  soils.  Some  data  bearing  upon 
these  points  are  given  in  the  table  1  below,  for  the  substances 
moderately  and  uniformly  packed  : 


VOLUME-WEIGHTS  OF 

Humus.3  Clay.  Quartz  Sand. 

•3349  l-ol°&  M485 

When  saturated  with  water,  the  same  substances  gave  the 
following  figures  : 

Air-dry.  Saturated  Increase. 

with  water.  °/0 

Humus2  .......  3565  1.1024  209.2 

Clay  ..........    '-0395  1.6268  55.9 

Quartz   sand..    1.4508  1.8270  25.9 

These  data  show  strikingly  the  effects  produced  by  the  sev- 
eral physical  soil  constituents  upon  some  of  its  physical  prop- 
erties. 

Chemical  Nature.  —  While  humus  artificially  produced  by  the 
action  of  caustic  alkalies  upon  sugar  or  cellulose  is  free  from 
nitrogen,  all  naturally  occurring  humus  contains  the  latter. 

It  is  not,  however,  present  in  the  form  of  ammonia,  as  it  cannot  be 
set  free  by  treatment  in  the  cold  with  lime  or  alkalies.  When,  how- 
ever, natural  humus  is  boiled  with  these  substances,  ammonia  is  slowly 
given  off,  but  the  process  continues  indefinitely  and  it  seems  to  be  im- 
possible to  expel  all  the  nitrogen  in  this  manner.  This  behavior  being 
characteristic  of  amido-compounds,  it  is  presumable,  in  view  of  the 
slightly  acid  nature  of  the  humus  substances,  that  natural  humus  is 
largely  of  an  amidic  constitution.  Artificial  humic  acid,  formed  by  the 

1  Wollny,  Zerset/une;  der  Organischen  Stoffe.  pp.  242.243. 

-  Peat  pulverized  and  extracted  with  alcohol  and  ether  to  remove  resinous  sub- 
stances. 


126  SOILS. 

action  of  caustic  alkalies  upon  sugar,  gums  or  cellulose,  combines  with 
ammonia  as  with  other  bases,  and  at  first  the  ammonia  can  be  readily 
expelled  from  this  as  from  other  ammonia  salts.  But  after  the  lapse  of 
some  time  it  seems  that  the  amidic  condition  is  assumed,  so  that 
caustic  lye  acts  but  very  slowly  and  cannot  expel  the  whole  of  the  nitro- 
gen present.  This  is  very  important  in  connection  with  the  practice 
of  fertilization,  as  any  ammonia  taken  up  by  or  generated  in  the  soil  is 
thus  in  the  course  of  time  rendered  comparatively  inert,  and  unavailable 
to  vegetation  until  nitrified. 

Progressive  Changes. — The  natural  neutral  humin  and 
ulmin,  as  found,  e.  g.,  in  the  lower  portions  of  peat  beds,  are 
in  the  course  of  time  by  oxidation  converted  into  ulmic  and 
humic  acids,  capable  of  combining  with  bases;  by  still  farther 
oxidation  they  form  apocrenic  and  crenic  acids,  readily  soluble 
in  water  and  in  part  forming  soluble  salts  with  lime,  magnesia 
and  other  bases.  These  acids  act  strongly  upon  the  more 
readily  decomposable  silicates  of  the  soil,  and  in  the  course  of 
time  may  dissolve  out,  and  aid  in  the  removal  by  leaching,  of 
most  of  the  plant-food  ingredients  as  well  as  the  ferric  hydrate 
of  a  soil.  Thus  red  or  rust-colored  soils  may  be  rendered  al- 
most white  by  continued  "  swamping  "  with  stagnant  water, 
and  be  greatly  impoverished ;  and  it  is  doubtless  largely  through 
this  agency  that  the  underclays  of  coal  beds  and  the  lower  por- 
tions of  peat  beds,  as  well  as  peat  and  coal  ashes,  are  almost 
wholly  destitute  of  mineral  plant  food. 

The  Phases  of  Humification. — The  progressive  changes  in- 
volved in  the  process  of  humification  of  vegetable  matter  are 
illustrated  in  the  table  below,1  together  with  the  farther  changes 
by  which  such  matter  may  ultimately  be  transformed  into  the 
several  varieties  of  coal,  and  finally  into  anthracite,  which  al- 
ready represents  nearly  pure  carbon,  but  in  nature  has  some- 
times been  still  farther  transformed  into  graphite  (black-lead) 
and  diamond. 

1  Data  recalculated,  omitting  ash. 


SOIL  AND  SUBSOIL. 


127 


PROGRESS  OF  IIUMIFICATION,  AND  FORMATION  OF  COAL. 
(MOISTURE  AND  ASH  OMITTKD  FROM  CALCULATIONS.) 


Oak  Wood. 

Peat.  » 

Coals. 

Cellu- 
lose. 

Fresh. 

De- 
cayed. 

Humin 
and 
Humic 
Acid. 

Brown 
Surface. 
(Ulmin.) 

Black. 

Lignite 
Brown 
Coal. 
(Bovey). 

Scotch 
Splint 
Bitu- 
minous. 

Penn'a 
Anthra- 
cite. 

40  in. 

80  in. 

Light 

Dark 

Brown. 

Brown. 

Carbon.  .  .  . 

44-44 

50.60 

53-r>° 

56.20 

49.41059.7 

57.80 

62.00 

64.  ,o 

69.50 

84.20 

94.80 

Hydrogen. 

6.17 

6.00 

5.20 

4.90 

2-5  "    4-5 

5.40 

5.20 

S.oo 

5.90 

5.80 

2.60 

Oxygen  .  .  . 

49-3*5 

35-8  "  47-3 

36.00 

30.70 

26.80 

24.00 

8.80 

I 

43-40 

41.20 

38.90 

V  2.60 

Nitrogen.  . 

-3  "  '8-7 

.80 

2.IO 

4.10 

.60 

i.  20 

} 

The  steady  increase  of  carbon  and  nitrogen,  together  with 
a  corresponding  decrease  of  oxygen,  are  well  illustrated  in  the 
analyses,  especially  in  the  strictly  comparable  series  of  peat 
samples  from  various  depths.  In  this  case  there  is  also  a  steady 
decrease  of  hydrogen,  and  an  increase  of  ash  from  2.72%  in 
the  surface  layer,  to  9.16  at  80  inches  depth.  This  increase  is 
due  in  the  main,  of  course,  to  the  progressive  volatilization  of 
the  organic  matter  in  the  forms  of  carbonic  dioxid  and  marsh 
gas  (median,  CH4). 

In  considering  this  table  it  should  not  be  forgotten  that 
while  normal  humus  stands  very  close  to  peat,  and  the  latter 
when  comprfrved  in  certain  stages  would  be  undistinguishable 
from  lignite  or  'mown  coal;  yet  both  peat  and  lignite  are 
known  to  be  formed  under  conditions  permitting  much  less 
access  of  air  or  oxygen  than  occurs  in  the  formation  of  normal 
black  soil-humus.  Hence  even  black  peat  cannot  at  once  stand 
in  place  of  soil-humus  when  removed  from  its  watery  bed,  but 
requires  considerable  time  and  aeration  (oxidation),  and  in 
most  cases  neutralization  with  lime  or  marl,  before  it  can  serve 
the  purposes  of  humus  in  the  soil. 

Lignite  and  the  progressively  more  carbonaceous  coals  are  and  have 
been  formed  under  the  conjoined  action  of  submergence  and  pressure, 
sometimes  also  aided  by  heat ;  and  thus  they  cannot  perform  the  func- 
tion of  soil-humus,  any  more  than  the  fire-clays  or  shales  underlying 


1  Detmer,  I.uiuhv.  Versuchst.,  Vol.  14,  1871. 


128 


SOILS. 


them  can  resume  their  original  soil-functions  without  prolonged  weather- 
ing. 

Amounts  of  Humus  and  Coal  Formed  from  Vegetable  Matter. — Only 
very  general  and  indefinite  estimates  can  be  given  of  the  amount  of 
humus  or  coal  formed  from  a  given  quantity  of  vegetable  matter,  since 
these  must  vary  according  to  the  conditions  under  which  the  transforma- 
tion occurs.  The  greater  or  less  access  of  air  and  of  moisture,  the 
temperature  and  pressure  under  which  the  process  occurs,  will  modify 
very  materially  the  quantitative  as  well  as  the  qualitative  result.  In 
the  hot  arid  regions  the  fallen  leaves  may  wholly  disappear  by  oxida- 
tion on  the  surface  of  the  ground,  while  under  humid  conditions  they 
are  mostly  incorporated  with  the  surface  soil.  If  we  assume  that  in 
the  humification  of  plant  debris  (estimating  their  average  nitrogen  con- 


FIG.  14. — Section  of  lignitized  log  showing  contraction  into  solid  lignite  on  drying. 

tent  at  i%),  no  nitrogen  is  lost,  it  would  seem  that  in  the  humid 
region  one  part  of  normal  soil-humus  might  be  formed  from  5  to  6 
parts  of  (dry)  plant  debris ;  while  in  the  extreme  regime  of  the  arid 
regions,  from  18  to  20  parts  of  the  same  would  be  required.  But  as 
most  probably  some  nitrogen  also  is  lost  in  the  process  of  humification, 
a  considerably  larger  proportion  of  original  substance  may  be  actually 
required. 

As  to  coal,  it  is  usually  assumed  that  it  requires  about  8  parts  of 
vegetable  matter  for  one  of  bituminous  coal.  Much  higher  estimates 
are  made  by  some,  and  an  observation  made  by  the  writer  at  the  Port 
Hudson  bluff,  Mississippi,  in  1869,  would  seem  to  justify  such  estimates. 
The  above  figure,  from  a  sketch  made  at  the  time,  shows  the  pro- 
portions to  which  a  pine  log  about  eight  inches  in  diameter  had  shrunk 


SOIL  AND  SUBSOIL. 


I29 


in  drying  into  a  small  sheet  of  lignitized  wood ;  the  original  trunk, 
projecting  from  a  bed  of  sand  some  forty  feet  below  the  surface,  being 
so  porous  and  spongy  that  when  wet  it  flattened  somewhat  by  its  own 
weight ;  it  was  connected  with  the  little  sheet  of  lignite  by  a  spirally 
twisted,  tapering  stipe. 

Here  evidently  the  proportion  of  lignite  formed  was  a  very  minute 
one,  doubtless  because  of  the  long  leaching  to  which  the  trunk  had 
been  subjected.  It  thus  seems  impossible,  as  in  the  case  of  humus, 
to  assign  any  definite  proportion  as  between  woody  matter  and  coal 
formed  from  it. 

Normal  humification  takes  place  only  under  the  influence  of 
moderate  temperature.  When  the  temperature  is  too  low,  bac- 
terial and  fungous  growth  are  repressed  or  arrested ;  when  too 
high,  the  fungous  vegetation  assumes  a  different  phase,  the 
result  of  which  is  the  almost  total  oxidation  of  the  organic 
matter,  sometimes  so  accelerated  as  to  initiate  rapid  com- 
bustion ("  fire-fanging  "  of  dung)  ;  leaving  in  any  case  but  a 
trifling  organic  residue  of  very  high  ash  contents.1 

Ercmacausis. — In  the  absence  of  a  sufficient  degree  of  mois- 
ture to  co-operate  with  the  other  agencies  of  humification.  the 
final  result  in  the  soil  is  practically  the  same  as  in  the  "  fire- 
fanging  "  of  dung.  The  organic  matter  is  almost  wholly  de- 
stroyed by  direct  oxidation  (eremacausis)  with  or  without 
the  aid  of  minute  organisms;  leaving  essentially  only  the  ash 
behind  to  he  reincorporated  with  the  soil.  This  is  to  a  very 
great  exte-nt  the  predominant  process  in  the  arid  regions  of  the 
Globe;  most  of  the  soils  formed  in  these  climates  being,  there- 
fore, very  poor  in  humus-substances,  and  deriving  it  almost 
entirely  from  the  decay  of  roots  only. 

The  extent  to  which  the  humus  of  a  soil  may  be  derived  from 
the  vegetable  debris  falling  or  growing  upon  the  surface,  varies 
greatly  with  the  climatic  conditions  as  well  with  the  nature  of 
the  soil.  In  the  forests  of  humid  climates  with  loamy  soils,  not 
only  does  the  autumnal  leaf-fall,  as  well  as  decaying  twigs  and 
trunks,  become  obviously  incorporated  with  the  surface  soil  as 

1  A  striking  illustration  of  this  is  afforded  by  Naegeli's  experiment  of  enclosing 
several  loaves  of  bread  in  a  loosely  closed  tin-box.  After  eighteen  months  there 
remained  only  seventeen  per  cent  of  air-dry  mouldy  matter,  totally  destitute  of 
starch. 

9 


130 


SOILS. 


decay  progresses  on  the  lower  surface,  but  active  animal 
agencies  (see  below)  carry  the  organic  remnants  bodily  down. 
But  where  heavy  clay  soils  prevail,  these  animal  agencies  are 
much  restricted  by  the  compactness  of  the  material;  only  a 
light  surface-layer  of  mold  would  be  formed,  and  the  humus 
of  the  lower  soil  layers  must  of  necessity  be  derived  from  the 
decay  of  the  roots  only.  This  origin  is  claimed  by  Kosticheff  1 
for  the  high  content  of  black  humus  in  the  tchernozem  or 
black  earth  of  Russia.  Following  Hellriegel  in  determining 
the  weight  of  roots  contained  in  successive  equal  layers  of  soil 
from  the  surface  downwards,  Kosticheff  gives  for  each  six 
inches  the  following  data  as  found  in  the  tchernozem,  taking  as 
100  the  root-content  of  the  surface  layer: 


Number. 

i 

i 

2 

2 

3 

3 

Depth. 

Roots. 

Humus. 

Roots. 

Humus. 

Roots. 

Humus. 

6  inches. 

IOO 

5-42 

IOO. 

8.ii 

IOO. 

9.64 

12 

89.1 

4.83 

63.9 

5-i9 

80.3 

7-77 

18 

66.9 

3.62 

48.3 

3-92 

70.0 

6.71 

24 

47-3 

2.56 

35-Q 

2.84 

584 

5.61 

3° 

47-3 

2.59 

26.0 

2.11 

38.2 

3-57 

36 

34-6 

1.88 

18.1 

1.47 

33-o 

3.18 

42 

23-9 

'  1.29 

6-3 

•51 

1  6.2 

1.56 

48 

14.4 

.78 

.70 

54 

6.7 

•36 

It  will  be  seen  that  there  is  a  very  close  correspondence  of  the  humus 
content  with  the  root  development  in  the  several  layers,  and  it  seems 
as  if  though  but  little  of  the  humus  could  be  derived  from  the  surface 
growth,  which  is  that  of  the  grasses  of  the  steppe. 

The  climate  of  the  black-earth  country  of  Russia  is,  though  not 
properly  arid,  yet  one  of  rather  deficient  and  uncertain  rainfall.  But  as  a 
consequence  of  extremely  arid  conditions,  and  in  sandy  lands,  it  may 
even  happen  that  the  immediate  surface  soil  contains  /ess  humus  than 
what,  in  the  farmers'  habitual  parlance,  would  be  called  the  subsoil ; 
because  of  the  penetration  of  slow  combustion  for  some  distance  into 
the  porous  soils.  It  will  then  be  lower  down  that,  in  the  presence  of  a 
favorable  degree  of  moisture  and  lower  temperature,  the  conditions  of 
normal  humification  are  fulfilled. 


1  Abstract  in  Ann.  de  la  Science  Agronomique,  Tome  2,  1887. 


SOIL  AND  SUBSOIL.  131 

It  is  not  always,  then,  that  the  commonly  recognized  distinc- 
tion between  surface  soil  and  subsoil  based  upon  humus  con- 
tent can  be  maintained.  But  the  observation  of  everything 
bearing  upon  this  point  is  of  the  utmost  importance  in  deter- 
mining both  the  agricultural  value  and  the  mode  of  treatment 
of  the  land. 

Losses  of  Humus  from  Cultivation  and  Fallowing. — The 
fact  that  humus  accumulates  in  woodlands  and  meadows, 
where  no  cultivation  is  given,  would  naturally  lead  to  the  con- 
verse conclusion,  viz.,  that  cultivation  causes  loss  of  humus  and 
of  its  constituents.  That  this  is  actually  the  case  is  recognized 
and  widely  acted  upon  in  practice,  and  there  is  no  question 
that  the  general  acceptance  of  stable  manure  as  the  most  widely 
useful  fertilizer,  despite  its  usually  low  content  of  plant-food 
ingredients,  is  based  upon  the  fact  that  it  supplies  vegetable 
matter,  in  a  condition  highly  favorable  to  its  conversion  into 
humus.  The  most  direct  and  cogent  proof  of  the  depletion  of 
the  soil  of  both  humus  and  nitrogen  by  continuous  cultivation 
of  cereal  grains  has  been  given  by  Snyder,1  who  determined 
the  loss  both  of  humus  and  of  nitrogen  suffered  by  a  Minnesota 
soil  during  eight  years'  continuous  cultivation  of  wheat.  The 
total  loss  of  nitrogen  was  1700  pounds  per  acre,  while  only 
350  pounds  were  utilized  by  the  crop;  about  1400  pounds  being 
dissipated  as  gas  or  leached  out  as  nitrates.  A  conservative 
estimate  of  the  loss  of  humus  suffered  during  the  same  period 
was  about  a  ton  per  acre  annually,  and  this  loss  seriously  de- 
creased not  only  the  nitrogen-content,  but  rendered  the  soil 
more  compact  and  less  retentive  of  moisture.  But  by  rotation 
of  the  wheat  with  clover  in  alternate  years,  very  nearly  an 
equilibrium  of  both  humus  and  nitrogen-content  was  obtained. 
In  addition,  the  amount  of  available  mineral  plant-food  was  de- 
creased by  continuous  grain  culture.  Ladd  has  made  similar 
observations  in  North  Dakota,  with  similar  results. 

That  excessive  aeration  results  in  serious  losses  of  humus 
as  well  as  of  nitrogen,  is  very  obvious  in  the  arid  region,  where 
it  is  the  habit  to  maintain  on  the  surface  of  orchards  and  vine- 
yards during  the  dry,  hot  summers,  a  thick  mulch  of  well- 
tilled  soil,  thus  preventing  loss  of  water  by  evaporation.  In 
the  course  of  years  this  surface  soil  becomes  so  badly  depleted 

1  Bull.  No.  70  Minn.  Kxp't  Station,  1905. 


132 


SOILS. 


of  humus  that  good  tilth  becomes  impossible,  the  soil  becom- 
ing light-colored  and  compacted ;  while  the  loss  of  nitrogen  is 
indicated  by  the  small  size  of  the  orchard  fruits.  Similar  losses 
are  of  course  sustained  in  the  practice  of  bare  summer-fallow, 
which  at  one  time  was  almost  universal  in  portions  of  the  arid 
region.  The  complete  extirpation  of  weed  growth  thus 
brought  about,  at  first  considered  an  unmixed  benefit,  has  ulti- 
mately had  to  be  made  up  for  by  the  practice  of  green-manur- 
ing; since  in  the  arid  region  the  use  of  stable  manure  en- 
counters many  difficulties. 

Estimation  of  Humus  in  Soils.  It  has  been  usual  to  determine  the 
amount  of  humus  in  soils  by  means  of  (dry  or  wet)  combustion,  cal- 
culating the  humus  from  the  carbonic  dioxid  so  formed,  while  measur- 
ing the  nitrogen  gas  directly.  But  in  this  process  the  entire  organic 
matter  of  the  soil,  humified  and  unhumified,  is  indiscriminately  in- 
cluded ;  and  it  is  wholly  uncertain  to  what  extent  the  latter  will  ulti- 
mately become  humus,  from  the  nitrification  of  which  plants  are  pre- 
sumed to  chiefly  derive  their  nitrogen.1  In  order  to  obtain  definite 
results,  the  actual,  functional  humus  must  be  extracted  from  the  soil 
mass  by  some  solvent  which  discriminates  between  the  humified  and 
unhumified  organic  matter.  This  cannot  be  done  by  direct  extraction 
with  caustic  soda  or  potash,  which  inevitably  dissolve  unhumified  mat- 
ters and  tend  to  expel  ammonia  from  the  humus ;  besides  themselves 
acting  as  humifiers  (see  this  chapter,  p.  125.) 

Grandeau  Method :  Matiere  Noire. — The  only  method  now  known 
which  accomplishes  this  separation,  practically  excluding  the  unhumi- 
fied while  fully  dissolving  the  humified  matter — is  that  of  Grandeau  :  the 
extraction  of  the  soil,  first  with  dilute  acid,  in  order  to  set  the  humic 
substances  free  from  their  combinations  with  lime  and  magnesia ;  and 
their  subsequent  extraction  with  moderately  dilute  solutions  of  am- 
monia (or  other  alkali  hydrates).  Upon  the  evaporation  of  the  am- 
monia-solution the  humus  is  left  behind  in  the  form  of  a  black  lustrous 
substance  ("  matiere  noire  "  of  Grandeau)  much  resembling  the  crust 
of  soot  formed  in  flues  from  wood  fires.  As  it  contains  a  variable 
amount  of  ash,  it  must  be  burnt  and  the  ash  subtracted  from  the  first 
weight. 

1  The  humus  determinations  thus  made,  which  include  nearly  all  those  made  by 
German  chemists,  give  the  humus-content  from  40  to  50°  0  too  high.  The  French 
determinations  are  mostly  made  by  the  method  of  Grandeau. 


SOIL  AND  SUBSOIL.  133 

Amounts  of  Humus  in  Soils. — While  in  peat,  marsh  and 
muck  lands  the  humus-content  may  rise  above  twenty  per 
cent,  in  ordinary  cultivated  lands  it  rarely  exceeds  about  five 
per  cent,  and  very  commonly  falls  below  three  per  cent,  even 
in  the  humid  regions.  In  properly  arid  soils  we  find  a  very 
much  lower  average,  rarely  exceeding  one  per  cent,  and  fre- 
quently falling  to  .30  and  even  less.  This  scarcity  of  humus 
manifests  itself  plainly  in  the  prevalently  light  gray  tint  of  the 
arid  soils. 

Meadows  and  woodlands  generally  show  the  highest  humus- 
content  in  their  surface  soils,  gradually  increasing  while  in  that 
condition;  while  when  taken  into  cultivation  the  humus-content 
gradually  decreases,  owing  to  the  free  aeration  and  consequent 
"  burning-out  "  caused  by  tillage.  Hence  the  humus  must  be 
from  time  to  time  replaced  by  the  use  of  stable  manure,  or 
green-manure  crops,  to  prevent  injurious  changes  in  the  tilling 
qualities  of  the  land.  Not  only  humus  as  such,  but  according 
to  Schloesing  also  the  insoluble  colloid  humates,  produce  in 
the  soil  a  loosening  effect  or  tilth  (Germ.  Bodengare),  which 
apparently  cannot  be  brought  about  by  any  other  substance.1 

Humates  and  Ulmatcs. — That  the  insoluble  humates  of  lime, 
magnesia,  iron,  manganese  and  alumina  are  present  in  most 
soils  is  conclusively  shown  by  the  composition  of  the  solution 
obtained  by  the  extraction  of  soils  with  weak  acid,  as  above 
mentioned  in  connection  with  the  quantitative  determination 
of  humus  according  to  Grandeau ;  since  these  bases  are  almost 
always  extracted  by  the  weak  acid.  When  the  brown  solution 
of  alkali  humate  obtained  in  this  process  is  carefully  neutralized 
with  sulfuric  or  hydrochloric  acid,  fir  is  mixed  with  solutions 
of  the  above  bases,  fiocculent,  insoluble  precipitates  are  formed, 
while  the  solution  is  discolored.  Similar  precipitates  may  be 
obtained  with  other  metallic  solutions,  notably  with  that  of 
copper,  which  precipitates  the  humus-acids  most  completely. 
Doubtless  these  compounds  contribute  greatly  to  the  conserva- 
tion of  the  humus-content  of  soils,  protecting  it  to  a  certain 
extent  from  oxidation,  rind  also  preventing  excessive  acidity. 
The  brown  tint  of  certain  subsoils  in  the  northern  humid  re- 

1  Tlie  decrease  of  humus  from  wheat  culture  in  the  soils  of  Minnesota  and  North 
Dakota  lias  been  studied  by  H.  Snyder  and  K.  V.  I. add,  respectively.  In  the 
prairie  lands  of  the  latter  State  the  total  organic  matter  in  the  first  six  inches  of 
soil  ranges  fram  15  to  as  much  as  26  ,  and  the  bumus  alone  from  4  to  7.8  0. 


I34  SOILS. 

gions  have  been  shown  by  Tollens  and  others  to  be  due  not  to 
ferric  hydrate,  as  had  been  supposed,  but  to  calcic,  magnesic 
and  aluminic  humates.  None  of  the  mineral  bases  or  acids 
present  can  be  detected  in  the  humic  solution  by  the  usual 
reagents. 

Mineral  Ingredients  in  Humus. — That  the  mineral  plant- 
food  ingredients  present  in  the  humus  extracted  by  the  Gran- 
deau  process,  and  which  remain  as  ash  when  the  matiere  noire 
is  burned,  are  capable  of  nourishing  plant  growth,  was  directly 
shown  by  Grandeau,  Snyder  and  others.  The  former  was  in- 
clined to  consider  that  those  substances  were  mainly  thus  taken 
up  by  plants,  under  natural  conditions.  This  theory,  however, 
has  not  been  sustained  by  subsequent  investigations ;  the  min- 
eral plant-food  thus  extracted  is  not  a  measure  of  the  immediate 
productiveness  of  the  soils,  as  demonstrated  by  Snyder,  and  the 
residual  soils  are  not  sterile.  It  is  also  still  doubtful  to  what 
extent  the  mineral  bases  and  acids  are  naturally  combined  with 
the  humus-substances,  it  being  contended  by  some  that  they  are 
brought  into  organic  combination  by  the  acid  and  ammonia 
extraction.  The  investigations  of  Snyder  and  Ladd,  above  re- 
ferred to,  prove  however  to  some  extent  at  least  that  the  humus- 
substances  are  naturally  combined  with  them,  and  that  prob- 
ably they  are  largely  made  available  to  plants  through  the 
direct  and  indirect  action  of  the  humus  compounds.  This  sub- 
ject is  farther  considered  in  chapter  19. 

The  nature  and  amounts  of  these  mineral  substances  are 
well  exemplified  in  the  subjoined  full  analysis  by  Snyder,  of 
the  ash  of  the  humus  and  humates  extracted  from  a  compound 
sample  of  prairie  soils  of  Minnesota,  which  had  been  thrown 
down  from  the  ammonia  solution  by  simply  neutralizing  the 
liquid : * 

ASH  OF  HUMUS  FROM  MINNESOTA  PRAIRIE  SOILS. 

Insoluble  matter  2 61 .97 

Potash  (K3O) 7.50 

Soda(Na3O) 8.13 

Lime  ( CaO) 0.09 

Magnesia  (MgO) 0.36 

Peroxid  of  Iron  (Fe2O3) 3.12 

Alumina  (Al^Os)    3.48 

Phosphoric  acid  (P.,O5) 12.37 

Sulfuric  acid  ( SO.,)   . .  .98 

Carbonic  acid  (,COa) 1.64 

1  Precipitation  with  an  excess  of  acid  does  not  greatly  change  the  results. 
3  In  California  soils  this  is  mostly  silica  soluble  in  carbonate  of  soda. 


SOIL  AND  SUBSOIL. 


135 


The  large  amounts  of  the  soluble  alkalies  potash  and  soda 
thrown  down  with  the  humic  matters  are  very  striking,  as  is 
the  very  large  proportion  of  phosphoric  acid.  Lime  and  mag- 
nesia had,  of  course,  been  mainly  eliminated  by  the  prelimi- 
nary acid  treatment. 

Functions  of  the  Unhumificd  Organic  Matter. — The  unhu- 
mified  plant  debris  in  the  soil  are  not  to  be  regarded  as  useless, 
even  aside  from  their  potential  conversion  into  active  humus. 
Not  only  do  these  remnants  of  vegetation  lighten  the  soil, 
rendering  it  more  pervious  to  air  and  water,  but  in  their  pro- 
gressive decay  they  give  off  carbonic  gas,  which  is  active  in 
soil-decomposition ;  and  they  serve  as  nourishment  to  the  soil 
bacteria  upon  which  its  thriftiness  so  greatly  depends.  See 
below,  chapter  9. 

The  Nitrogen-Content  of  Humus. — Since  soil-humus  is 
doubtless  the  chief  depository  of  soil-nitrogen,  and  the  main 
source  from  which,  through  the  process  of  nitrification,  the 
nitrogen-supply  to  plants  is  usually  derived,  its  content  of  that 
element  is  a  matter  of  great  interest.  It  has  been  customary 
to  estimate  approximately  the  nitrogen-content  of  soils  by  the 
proportion  of  humus-substance  present ;  and  as  the  light  tints 
of  the  soils  of  the  arid  region  indicate  a  small  humus-content, 
a  scarcity  of  nitrogen  seemed  to  be  also  indicated  for  these 
lands.  As  this  in  a  number  of  cases  did  not  seem  to  accord 
with  actual  experience,  an  investigation  of  the  subject  was 
made  at  the  California  experiment  station,1  with  the  results 
shown  in  the  subjoined  table.  In  considering  these  results  it 
must  be  kept  in  mind  that  while  arid  conditions  can  rarely  be 
fulfilled  in  the  humid  region,  humid  conditions  are  quite  fre- 
quently locally  represented  in  the  arid,  in  lowlands  and  on  high 
mountains;  while  moderately  moist  benchlands  represent  the 
semi-arid  regime. 

1  Hilgard  and  J,i_t]\t.  On  the  \itrogen-content  of  Soil-humus  in  the  Humid  and 
Arid  regions.  Rep.  Cal.  Kxp't  Station  for  1892-4;  Agric.  Science,  April,  1894; 
Wollny's  Forsch.  Geb.  Agr.  I'hys.,  1894. 


136 


SOILS. 


HUMUS    PERCENTAGE  ANT)    NITROGEN  CONTENT   IN   SOILS  OF  THE   ARID 
AND  HUMID  REGIONS. 


1  Station 

Number 

Soils  arranged  in  order  of  nitrogen  percentages  in 
humus. 

C        .J 
*"        ~ 
2—  "  u 
Eo  u 
_  w  >- 

3            a> 

X     o- 

Nitrogen 
in  Humus, 
per  cent. 

Nitrogen 
in  soil, 
per  cent. 

9061 

2291 
1904 
1901 
704 
6 
1679 

2324 
1167 

1536 

1126 

2301 
1607 

"59 
1900 
1113 

"49 

1538 
"47 
2403 
1281 
1117 
1406 

1172 
1958 
1423 

1291 

585 
863 
1907 
1115 

332 
2126 
1910 
2187 
1759 
774 
1984 
2325 
igoC 
2430 

SOILS  OF  THE  ARID  REGION  (California). 

Dark  clay  loam,  Arroyo  Grande  Valley,  San  Luis  Obispo 
County  

3.06 

•71 
.90 
.64 

.00 

1.05 

1.  20 

.38 

1.66 

.20 

.1? 

.25 

•37 
.84 

•54 

•47 
.65 
.66 

':S 

.80 

•3° 

.72 

•85 

•39 

.76 

I.OO 

2.89 
.92 
.85 
.28 
.62 
1.64 
•97 
•53 
1.29 

$ 

•95 
1.85 

22.OO 
21.10 

19.50 
18.75 

18.66 
18.66 
18.58 
18.40 
18.19 

18.00 
17.27 
16.90 
1  6.80 
16.75 
16.65 
I6.6o 

16.18 
1  6.08 
1  6.06 
16.00 
15.50 
15.27 

15.00 

14-75 
14.45 

14-3° 
14-34 
14.10 

I3-91 
13.26 
13.20 
12.50 
11.75 

II.  21 
I  I.IO 
II.O4 
10.85 
10.50 
IO.7O 
9.80 
8.70 

.670 
.150 
.180 
.I2O 
.112 
.106 
.203 
.070 
.302 

.036 
.095 

•'37 
.042 
.062 
.140 
.090 

.074 
.105 
.106 
.240 
.090 

•'23 

-°45 
.106 

.122 

.056 
.IO9 
.146 
.402 
.121 
.112 

•°35 
.070 
.183 

.1  10 

.059 
.140 
.060 
.070 

•°93 
.160 

Red  soil,  Orland,  Glenn  Co  

Sediment  Soil,  Porterville,  Tulare  Co  

Sandy  soil  near  Ceres,  Stanislaus  Co.      .          .        .        .. 

Sandy  soil  of  plains,  near  Fresno,  Fresno  Co  

Black  adobe  soil,  Stockton,  San  Joaquin  Co  

Black  adobe  soil,  Berkeley,  Alameda  Co  

Clay  soil  of  desert,  Imperial,  San  Diego  Co  

Black  clay  loam  soil,  near  Tulare,  Tulare  Co  

Brown  loam  soil,  Windsor   Tract,    Riverside,  Riverside 
County  

Sandy  loam  soil,  Paso  Robles,  San  Luis  Obispo  Co.  .  .  . 
Red  hill  soil,  Upper,  Lake,  Lake  Co                 .      .        ... 

Plateau  soil  of  desert,  Lancaster,  Los  Angeles  Co  

Sandy  plains  soil,    Tulare,  Tulare  Co  

Sandy  soil,  near  Modesto,  Stanislaus  Co  

Clay  loam  soil  (slate),  Jackson,  Amador  Co.       .        ... 

Adobe  clay  soil,  near    Paso  Robles,   San    Luis    Obispo 
County  

Mesa  soil,  Chino,  San  Bernardino  Co.                       .  . 

Sandy  loam  soil,  Paso  Robles,  San  Luis  Obispo  Co.  .  .  . 
Valley  Soil,  Wheatland,  Yuba  Co  

Red  Mesa  soil,  Pomona,  San  Bernardino  Co  

Sandy  granitic  soil,  near  Jackson,  Amador  Co  

Red  loam  soil,  Arlington  Heights,  Riverside,  Riverside 
County  

Red  clay  loam  soil,  east  of   Tulare,  Tulare  Co  

Sandy  Mesa  soil,    Nipomo,  San  Luis  Obispo  Co  

Chocolate-red    soil,    Carisa     plain,    San    Luis     Obispo 
County  .    .            

Sandy  hill  land,  near  Jackson,  Amador  Co  

Wire-grass  loam  soil,  Visalia,  Tulare  Co  

Red  ridge  loam  soil,  Grass  Valley,  Nevada  Co   

Dark  loam  soil,  near  Chino,  San    Bernardino  Co  

Sandy  granitic  soil,  near  Jackson,  Amador  Co  

Plateau  desert  soil,  Mojave,  Los  Angeles  Co  

Gravelly  soil,  East   Highlands,  San  Bernardino  Co  
Ojai  Valley  soil,  Nordhoff,  Ventura  Co  

Sandy  loam  soil,  Soledad,  Monterey  Co  

Sandy  soil,  Perris  Valley,   Riverside  Co  

Bench  slope  soil,  Ontario,  San   Bernardino  Co  

Red  soil,  East  Highlands       "              "             "  

Silt  soil  of  desert,  Imperial,  San  Diego  Co  

Light  sandy  soil,  Pomona,  San  Bernardino  Co  

Hillside  adobe,  Berkeley,  Alameda  Co  

Average  of  arid  uplands  

.91 

!5-23 

•135 

SOIL  AND  SUBSOIL. 


137 


HUMUS    PERCENTAGE    AND    NITROGEN  CONTENT    IN    SOILS   OF   THE   ARID 
AND    HUMID   REGIONS. 


Station  | 
Number 

Soils  arranged  in  order  of  nitrogen  percentages  in 
humus. 

Humus  in 
soil, 
per  cent. 

£  3  •£ 

bfl  5  v 
030 

.Sac  5 

X  a  a 

c 

Hi 

g-Sfc 

586 
1466 
1284 
1148 
1714 

77 
1880 

1903 
1  68 
1760 
506 
1636 
1758 

'963 
2080 

207 
23'9 
213 
1704 
2295 

I  10 

37 
26 

23 

27 

SUB-IRRIGATED  ARID  SOILS  (California). 
Sandy  plains  soil,  Tulare,  Tulare  Co  

1.14 
.60 
1.99 

1.16 

.78 

•47 
1.19 

1.  12 

.84 
.91 

•75 

2.OO 

.60 

•36 

1.64 

10.79 

10.66 
10.20 
9.65 
9.56 

9-37 
8.90 
8.50 

7-99 

7.70 

7-47 
6.86 
6.83 
6.05 
5o6 

.123 

.064 

.203 

.1  12 

.074 
.045 
.109 
.140 
.067 
.070 
.050 

•'37 
.071 

.022 
.OOXD 

I  -oam  soil,  Miramonte,    Kern   Co  

Moist  land  loam  soil,  Chino,    San  Bernardino  Co  

Swale  soil,  near  Paso  Kobles,  San  Luis  Obispo  Co  
Bench  soil,  Santa  Clara  River,  Piru,  Ventura  Co  

Alluvial  soil,  Tulare  Lake  bed,  Tulare  Co  

Creek  bench  soil,    Niles,  Alameda  Co      

Sediment  soil,    Porterville,  Tulare  Co  

Alluvial  soil,  Santa  Clara  river,  Santa  Paula,  Ventura  Co 
(ireen-sage  land,  Perris  Valley,  Riverside  Co  

Alluvial  soil,  Colorado  River,  Yuma,  San  Diego  Co.... 
Red  soil,  Manton,    Tehama  Co  

Alkali  soil,  Perris  Valley,    Riverside  Co  .. 

Sandy  loam  soil,  Willows,    Glenn    Co  

Sandy  soil,  Santa   Maria  Valley,  Santa  Barbara  Co  
Average  of  sub-irrigated  arid  soils  

1.  06 

1.25 

7-83 
1.54 

•94 
1.70 
1.71 

2.28 

8.38 

6.96 
6.70 
6.36 

5-2i 
4.50 
4.25 

3-°7 

.099 

.085 
.514 
.089 
.049 

•0/7 
.072 
.070 

HUMID    SOILS    FROM    ARID    AND   HUMID    REGIONS 

(California). 
Eel  River  Alluvial  soil,  Ftrndale,  Ilumboldt  Co  

Alluvial  soil,  I  lupa  Valley,  1  1  u  in  bold  t  Co  

Marsh  soil,  Novato,  Meadows,    Marin  Co  

Valley  soil,  I  lollister,  San    Benito  Co  

Tule  soil,  Upper  Lake,    Lake  Co  .        

Alluvial  soil,  Putah  Creek,  Dixon,  Solano  Co  

Redwood  Valley  soil,  Pescadero,  San  Mateo  Co  

Average  for  California  

2.45 

2  33-02 

5-07 
13.84 

2-13 

5.29 

6.08 

4.20 

3-49 
3.66 

•'35 

22.OI2 
.218 

.483 
.184 

OTHER    STATES. 

Bog  soil,  Michigan  

Hack-land  clay  loam,  I  fouma,  Louisiana  

Duff  soil,  Oregon    

Sandy  prairie  soil,  Harris  Co.,  Texas  

Average  for  other  States  

7.01 

'•57 

9-95 

3.01 

0.07 
6.17 

3-78 

5-°7 
1.71 
6.07 

2-13 

2.54 

•295 

.078 
.IJO 

•237 
.286 

.!.)(. 

Red  soil,  Oahu  Island,  I  lawaii    maximum  )  
(itiava  soil,  I  lawaii  Isl.ind  (minimum  

Average  of  5  soils,  (  )ahu  Island  

Average  of  2  soils,  Maui  Island  

Average  of  4  soils,  I  lawaii  Island  

Average  for  Hawaiian  Islands  

5.26 

3.6')         .K") 

Total  for  Humid  soils,  averace..  . 

4.s8    '      A.  2  \          .l6t) 

2  Introduced  only  for  comparison  of  the  nitrogen  percentage  in  Humus  and  not 
included  in  the  average. 


138  SOILS. 

It  thus  appears  that  on  the  average  the  humus  of  the  arid 
soils  contains  about  three  and  a  half  times  as  much  nitrogen  as 
that  of  the  humid ;  that  in  the  extreme  cases,  the  difference  goes 
as  high  as  over  six  to  one  (see  Nos.  37  and  704) ;  and  that  in 
the  latter  cases,  the  nitrogen-percentage  in  the  arid  humus  con- 
siderably exceeds  that  of  the  albuminoid  group,  the  flesh-form- 
ing substances. 

It  thus  becomes  intelligible  that  in  the  arid  region  a  humus- 
percentage  which  under  humid  conditions  would  justly  be  con- 
sidered entirely  inadequate  for  the  success  of  normal  crops,  may 
nevertheless  suffice  even  for  the  more  exacting  ones.  This  is 
more  clearly  seen  on  inspection  of  the  figures  in  the  third 
column,  which  represent  the  product  resulting  from  the  multi- 
plication of  the  humus-percentage  of  the  soil  into  the  nitrogen- 
percentage  of  its  humus ;  as  appears  in  comparing  the  respective 
averages,  or  Nos.  1167  and  no  and  others.  An  additional 
consideration  is  the  probable  greater  ease  with  which  the  nitri- 
fying bacteria  can  act  upon  a  material  so  rich  in  nitrogen. 

We  must  not,  then,  be  misled  by  the  smallness  of  many 
humus-percentages  in  the  arid  region,  into  an  assumption  of  a 
deficiency  in  the  supply  of  soil-nitrogen. 

Decrease  of  Nitrogen- Content  in  Humus  with  Depth. — Since  the 
oxidation  of  the  carbon  and  hydrogen  in  the  humus- substance,  and  the 
consequent  increase  of  its  relative  nitrogen-content,  are  manifestly  de- 
pendent upon  the  presence  of  air  and  heat,  it  is  reasonably  to  be 
expected  that  the  nitrogen- percentage  of  the  humus  should  decrease 
with  the  depth  of  the  soil.  That  this  is  really  the  case  is  plainly  shown 
in  the  subjoined  table,  which  gives  the  humus-percentages  and  the 
nitrogen-content  of  the  humus  from  the  surface  foot  down  to  twelve  feet, 
in  a  soil  on  the  bench  of  the  Russian  River,  Cal.,  which  is  sub-irrigated, 
and  liable  to  more  or  less  rainfall  during  the  summer.  It  will  be  seen 
that  not  only  does  the  absolute  humus-percentage  decrease  quite  regularly 
down  to  seven  feet,  at  which  point  there  evidently  was  at  one  time  a 
strong  root  development,  causing  a  notable  increase  of  the  humus-con- 
tent ;  from  which  again  there  is  a  regular  decrease  down  to  the  twelfth 
foot.  It  will  be  noted  that  the  nitrogen-percentage  in  the  humus, 
while  not  decreasing  with  the  same  regularity  as  the  humus-content 
itself,  yet  exhibits  a  general  recession  from  5.30  to  1.15  in  the  ninth 
foot,  to  which  direct  oxidation  doubtless  never  penetrates. 


SOIL  AND  SUBSOIL.  139 

HUMUS    AND   NITROGEN-CONTENT   OF    RUSSIAN    RIVER    SOIL. 


Depth  in  feet. 

Per  cent  Humus  in 
soil. 

Per  cent  Nitrogen  in 
Humus. 

Per  cent  Humus- 
Nitrogen  in  soil. 

i 

1.  21 

5-3° 

.064 

2 

1.16 

4-32 

•  054 

3 

1.14 

3-87 

.044 

4 

LI? 

3-76 

.044 

I 

•74 
.60 

2.16 
2.66 

.016 
.016 

7 

•47 

2-54 

.012 

8 

.78 

i-54 

.OI2 

9 

•54 

2.24 

.OI2 

10 

.52 

i-i5 

.O06 

ii 

•53 

I-5I 

.008 

12 

•  44 

1.81 

.008 

Influence  of  the  Original  Materials  on  the  composition  of 
Humus. — The  great  variability  of  the  composition  of  humus 
formed  from  different  substances  is  well  shown  in  the  sub- 
joined table,  representing  the  results  of  experiments  made  by 
Snyder,1  who  caused  various  substances  to  humify  by  mixing 
the  pulverized  material  intimately  with  a  soil  poor  in  humus, 
and  allowing  the  process  to  continue  for  a  year.  At  the  end 
of  that  time  the  humus  formed  was  extracted  by  the  method 
of  Grandeau,  outlined  above,  and  analyzed,  with  the  following 
results. 


Sugar. 

Oat 
Straw. 

Green 
Clover. 

Wheat 
Flour. 

Saw- 
dust. 

Meat 
Scraps. 

Cow 

Manure.8 

Carbon  
Hydrogen  
Nitrogen  

57.84 
3-04 
.08 

54-30 

2.48 

2.  qo 

54.22 

3-40 
8.24 

51.02 
3.82 
S.O2 

40.28 
3-33 

O.  72 

48.77 

4-3° 
10.96 

4'-93 
6.26 
6.16 

Oxygen  

7O.O.1 

40.72 

-54.14 

40.14 

4/.O7 

•3  C.Q7 

4^.6; 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

While  it  may  be  questioned  whether  the  process  of  humifica- 
tion  had  in  these  materials  really  reached  the  point  of  sensible 
completion  in  all  cases  (notably  in  those  of  sawdust  and  cow 

1  Bull.  No.  5 "5,  Minn.  Kxp't  Station,  p.  12,  Chem.  of  Soils  and   Fertilizers,  p.  94. 

2  The  figures  for  cow  manure  are  so  far  out  of    range    with    any  cithers   thus   far 
observed,    that    it    seems    reasonable   to    suppose  that  they  are  influenced  by  un- 
changed substances  present  in  the  excreta. 


140 


SOILS. 


manure),  the  great  variability  of  the  products  from  different 
materials  is  very  striking.  When  the  nitrogen-content  is  de- 
ducted the  percentage  composition  of  the  products  agrees 
more  nearly.  Considering  that  the  nitrogen  is  probably  pres- 
ent in  the  amid  form,  it  is  natural  that  hydrogen  should  in  a 
measure  vary  with  it,  as  in  the  case  of  the  clover,  flour  and 
meat  humus.  Nitrogen  being  the  most  variable  ingredient  of 
humus,  it  seems  probable  that  the  variation  of  the  proportion 
of  the  humus-amids  present  is  the  most  potent  factor  in  the 
variability  of  the  composition  of  natural  soil-humus. 

Arranging  these  results  in  the  order  of  their  nitrogen-con- 
tent as  in  the  table  below,  we  see  that  the  latter  approximately 
corresponds  to  the  original  protein-content  of  the  humified  sub- 
stances. 

Humus  from  meat  scraps 10.96  °J0  Nitrogen. 

"         "     green  clover 8.24 

"         "     cow  manure 6.16 

"         "     wheat  flour 5.05 

"         "     oat  straw 2.50 

"         "     sawdust 32 

While  the  above  data  prove  the  correlation  between  the  first 
products  of  humification  and  the  original  substance,  it  must  be 
remembered  that  subsequently,  under  proper  conditions,  the 
nitrogen-percentage  in  humus  may,  in  the  course  of  time,  in- 
crease very  greatly,  even  to  a  proportion  considerably  above 
that  contained  in  flesh  itself.  When  we  consider  that  ordina- 
rily, the  latter,  and  the  albuminoid  substances  generally,  decom- 
pose in  contact  with  air  with  an  abundant  evolution  of  ammonia 
compounds,  sometimes  leaving  only  a  little  fat  (adipocere) 
behind,  it  is  surprising  that  the  decomposition  within  the  soil 
should  have  exactly  the  opposite  result,  viz.,  an  accumulation 
of  the  nitrogen.  The  causes  of  this  marked  difference  are  not 
yet  well  understood,  but  it  is  probably  due  to  the  differences 
in  the  kinds  of  bacteria  that  are  active  in  the  two  cases. 

Snyder  has  also  shown  that  the  richer  the  organic  matter 
humified  is  in  nitrogen,  the  more  energetically  it  acts  in  render- 
ing available  the  mineral  matters  of  the  soil  for  plant  nutrition. 


SOIL  AND  SUBSOIL.  I4! 

Correspondingly,  Ladd  1  has  shown  that  with  the  increase  of 
humus  in  the  soil,  there  is  also  a  corresponding  increase  in  the 
amounts  of  mineral  plant-food  extracted  from  the  soil  by  a 
four  per  cent  solution  of  ammonia,  such  as  is  employed  in  the 
Grandeau  method  of  humus-determination. 

1  Bull.,  S.  Dakota  Station,  Nos.  24-32,  35,  47. 


CHAPTER  IX. 

SOIL  AND  SUBSOIL  (Continued], 

ORGANISMS   INFLUENCING  SOIL  CONDITIONS;  BACTERIA,   ETC. 
MICRO-ORGANISMS  OF  THE  SOIL. 

INTIMATELY  correlated  with  the  humus-substances  of  the 
soil,  as  well  as  with  its  temporary  contents  of  the  carbohydrates 
(cellulose,  gums  and  sugars)  from  which  humus  is  formed, 
is  the  multitudinous  flora  of  micro-organisms  always  present 
and  exercising  important  functions  in  connection  with  the 
growth  of  the  higher  plants.  Extended  researches  by  Adametz, 
Schloesing  and  Miintz,  Miquel,  Koch,  Fraenkel,  Winograd- 
sky,  Frank  and  many  others,  have  thrown  light  upon  the  im- 
mense numbers  and  great  variety  of  minute  organisms,  es- 
pecially of  the  bacterial  group,  present  in  soils,  and  upon  their 
distribution  and  activities  in  the  same.  It  has  been  shown 
that  their  numbers  are  greatest  near  (although  usually  not 
at)  the  surface,  decreasing  rapidly  downward  and  generally 
disappearing  wholly  at  depths  between  seven  and  eight  feet; 
the  latter  depth  varying  of  course  according  to  the  nature 
and  porosity  of  the  soil,  and  both  depth  and  numbers  being 
greatest  in  summer. 

Numbers  of  Bacteria  in  Soils. — Adametz  found  in  one  gram 
of  soil,  38,000  bacteria  at  the  surface,  460,000  at  ten  inches 
depth ;  in  a  loam  soil  at  the  surface  500,000,  at  ten  inches  464,- 
ooo  in  each  gram  of  earth.  Of  mould  and  similar  fungous 
germs  there  were  only  40  to  50  in  the  same,  6  species  being 
true  molds,  while  four  were  ferments,  including  the  yeasts  of 
wine  and  beer.  Fraenkel  found  in  virgin  land  from  near  Pots- 
dam, a  sudden,  marked  decrease  at  depths  of  from  three  to 
five  feet;  while  in  earth  from  inhabited  places  within  the  city  of 
Berlin,  considerable  numbers  were  still  present  at  eight  and 
even  ten  feet,  in  some  cases. 

In  the  researches  lately  made  by  Hohl  at  the  bacteriological 

142 


SOIL  AND  SUBSOIL. 


143 


station  at  Liebefeld,  near  Bern,  it  was  found  that  in  cultivated 
soils  the  number  of  bacteria  greatly  exceeds  the  figures  given 
by  Fraenkel.  He  found  a  gram  of  moist  soil  to  contain  from 
three  to  fifteen  millions  of  bacteria.  In  the  cultivated  soil  of 
Liebefeld  he  found  5,750,000,  in  meadow  land  9,400,000,  in  a 
manure  pile  44,500,000  per  cubic  centimeter.  These  figures 
seem  high  for  so  small  a  quantity  of  material,  but  taking  the 
average  size  of  a  bacterium,  a  cubic  centimeter  might  readily 
contain  six  hundred  millions.  (Grandeau,  Ann.  Sci.  Agrono- 
mique,  vol.  i,  p.  461,  1905). 

Mayo  and  Kinsley  (Rep.  Kansas  Exp't  Station  for  1902-3)  have 
made  elaborate  investigations  of  the  numbers  and  kinds  of  bacteria 
found  in  various  soils  in  Kansas,  in  connection  with  different  crops. 
It  is  noteworthy  that  in  most  cases  their  figures  exceed  considerably 
those  given  by  European  observers,  as  they  often  reach  high  into  the 
millions,  in  one  case  to  over  fifty  millions,  per  cubic  centimeter.1 

Five  fields  with  different  soils  were  investigated ;  the  land  being 
described  as  follows  :  "  Field  No.  i  is  a  black  loam  containing  con- 
siderable humus ;  field  No.  2  is  similar  to  field  i  but  contains  more 
humus ;  field  No.  3  is  a  thin  soil  with  clay  gumbo  subsoil ;  fields  Nos.  4 
and  5  are  black  loams,  but  not  as  rich  in  humus  as  either  No.  i  or 

No.  2." 

The   average  bacterial  contents  of   the   several  fields  are  given  as 

follows  : 

Field  No.  i 33, 93 !  .747  Per  cubic  centimeter. 

«     No.  2 53,596,060     "       "  " 

"     No.  3 78,534     "       " 

"     No.  4 8,643,006     "       "  " 

"     No.  5 3.192,131     "       " 

"The  crop  records  of  these  fields  for  the  past  ten  years  indicate 
that  the  crop  yield  has  been  (more  or  less  ?)  directly  proportional  to 
the  bacterial  content  of  the  soil  of  each  field ;  field  2  has  produced  the 
largest  yield,  field  3  the  least." 

Unfortunately  no  chemical  analyses  of  any  of  these  soils  are  com- 
municated ;  but  at  the  request  of  the  writer  samples  of  the  soils  of  the 

1  The  mode  of  statement  in  the  paper  is  not  always  quite  clear  as  to  the  manner 
in  which  the  averages  given  were  calculated.  It  must  be  remembered  that  these 
data  refer  to  cubic  centimeters  of  soil,  or  about  twice  the  amount  (t  gram)  used 
by  European  observers. 


144 


SOILS. 


first  three  fields  were  sent  from  the  Kansas  station  for  humus  deter- 
minations (courteously  made  by  Dr.  H.  C.  Myers),  which  gave  the 
following  results : 

Field  No.  i 2.19%  of  Humus. 

"     No.  2    3-07%   "         " 

"     No.  3 1.85%  "         " 

While  these  humus-percentages  are  not  directly  proportional  to  the 
bacterial  content,  a  favoring  effect  of  high  humus-content  is  clearly 
shown.  The  bacterial  and  the  humus-content  of  these  soils  are  sensibly, 
even  if  not  directly,  correlated ;  which  might  reasonably  be  expected, 
since  the  organic  matter  and  the  humus  are  the  bacterial  food. 

The  investigation  also  showed  wide  differences  in  the  bacterial  con- 
tent of  the  same  soil  when  different  crops  were  growing  on  it.  Thus  in 
samples  taken  on  Aug.  15,  there  were  found  in  the  first  twelve  inches  of 
a  black  loam  soil  bearing  timothy  and  clover,  1,380,000,  in  the  same 
with  alfalfa  and  clover,  21,091,000,  with  maize  from  one  to  over  two 
millions.  In  soils  from  the  western  part  of  Kansas,  the  bacterial  con- 
tent of  the  same  crops  was  much  less  (as  doubtless  is  the  humus-con- 
tent), and  it  is  noteworthy  that  the  prairie  buffalo  grass  shows  through- 
out a  relatively  high  bacterial  content  in  the  first  foot  of  the  soil,  ranging 
next  to  alfalfa.  The  root  bacteria  living  on  the  legumes  will  naturally 
increase  the  bacterial  content  of  the  soils  on  which  they  grow,  more 
than  plants  which,  like  maize,  do  not  directly  utilize  bacterial  action. 

Multiplication  of  the  Bacteria. — Marshall  Ward  and  Duclaux  have 
made  some  special  observations  in  regard  to  the  rapidity  with  which 
certain  bacteria  multiply.  Duclaux  summarizes  the  final  conclusion 
thus :  taking  as  a  basis  the  time  of  35  minutes  for  the  subdivision  into 
two,  which  has  been  frequently  observed  by  Ward,  there  would  be  four 
millions  of  bacteria  produced  in  twelve  hours.  The  first  filaments  had 
plenty  of  room  in  a  drop  culture  of  one  cubic  millimeter ;  but  at  the 
end  their  total  volume  amounted  to  the  tenth  part  of  the  total  volume 
of  the  drop.  At  the  above  rate,  making  48  generations  in  24  hours, 
281,500  billions  of  organisms  would  be  produced.  (Grandeau,  Ann. 
Sci.  Agron.  Vol.  i,  1905,  p.  456). 

Aerobic  and  Anaerobic  Bacteria. — As  may  readily  be  in- 
fe"red,  the  cultural  and  other  surface  conditions  exert  a  potent 
influence  both  upon  the  kinds  and  abundance  of  the  bacteria 
and  molds;  since  the  life- functions  of  some  are  dependent  upon 


SOIL  AND  SUBSOIL,  14$ 

the  presence  of  free  oxygen  ("  aerobic  "),  while  others  flour- 
ish best,  or  only,  in  the  absence  of  air  ("  anaerobic  "),  or  are 
able  to  avail  themselves  of  the  presence  of  combined  oxygen, 
by  reduction  of  oxicls  present.  Their  number  is  found,  in 
general,  to  be  greatest  in  cultivated  lands,  and  bacteria  are 
there  by  far  predominant  over  the  moulds.  On  the  other  hand, 
the  moulds  gain  precedence  in  woodlands  and  meadows,  at  least 
so  far  as  air  can  gain  access;  while  in  the  deeper  layers  of  the 
same,  as  well  as  in  peaty  lands,  bacterial  life  is  always  scanty. 
This  holds  particularly  in  respect  to  the  nitrifying  organisms, 
and  others  whose  life-functions  are  dependent  upon  abundant 
access  of  oxygen  (aerobic). 

Food  Material  Required. — All  bacteria,  like  the  fungi,  are 
dependent  for  their  development  upon  the  presence  of  adequate 
amounts  of  some  organic  food-material,  best  apparently  in 
water-soluble  form.  In  the  soil  it  seems  to  be  chiefly  com- 
pounds of  the  carbohydrate  group,  especially  various  gums 
derived  from  the  decaying  plant  substance,  or  from  stable  ma- 
nure;  in  artificial  cultures,  glucose  is  mostly  found  to  be  a 
highly  available  food.  When  the  decaying  substance  reaches 
the  state  of  humus,  the  latter  seems  to  be  available  as  food 
only  to  comparatively  few  bacteria.  The  very  abundant  de- 
velopment of  bacterial  life  seems  to  be  among  the  most  im- 
portant effects  produced  by  stable  manure  upon  the  surface 
soil,  in  establishing  good  tilth  ("Bodengare"  in  German). 

Functions  of  the  Bacteria. — While  there  is  still  much  uncer- 
tainty as  to  the  exact  functions  performed  by  most  of  these 
bacteria  in  respect  to  soil-formation  and  plant  growth,  there 
are  several  kinds  whose  activity  has  been  proved  to  be  of  the 
utmost  importance  in  one  or  lx>th  directions;  it  having  been 
shown  that  when  the  soil  is  sterilized  cither  by  heat  or  anti- 
septic agents,  certain  essential  processes  are  completely  sup- 
pressed until  the  soil  is  re-infected  and  the  conditions  of  bac- 
terial life  restored. 

Probably  the  chief  in  importance  are  those  connected  with 
the  processes  of  nitrification  and  dcnitrification,  bearing  as  they 
do  upon  the  supply  to  plants  of  the  most  costly  of  the  three 
substances  furnished  by  fertilizers.  These  organisms  have 
been  first  extensively  studied  by  Winogradsky,  while  the  con- 
10 


146 


SOILS. 


FIG.  15.— Nitrosomonas.     (Winogradsky). 


,,.  -:-.- 


ditions  of  their  activity  have  been  largely  developed  by  R. 

Warington. 

Nitrifying  Bacteria. — The  conversion  of  ammonia  into  ni- 
trates is  accomplished  under 
proper  conditions  by  two  or- 
ganisms, or  groups  of  organ- 
isms; the  first  stage  being  the 
formation  of  nitrites  by  the 
round,  often  flagellate  cells  of 
nitrosomonas  (or  nitrosoco- 
cus).  The  second,  the  oxid- 
ation of  the  nitrites  into  ni- 
trates by  very  minute  rod- 
shaped  bacilli,  named  nitrobac- 
teria.  The  conditions  under 
which  these  bacteria  can  act 
are  quite  definite  in  that,  aside 

FIG.  i6.-Nitrobacterium.  (Winogradsky).         from   3.  SUpply   of  the   nitHfiable 

substance,  a  fairly  high  temperature  (24°  C.  or  75°  F.)  and 
a  moderate  degree  of  moisture,  there  must  be  a  free  access  of 
oxygen  (air)  ;  and  there  must  be  present  a  base  (or  its  car- 
bonate) with  which  the  acids  formed  by  oxidation  can  imme- 
diately unite.  In  an  acid  medium  ("sour"  soils)  nitrifica- 
tion promptly  ceases ;  as  it  also  does  whenever  the  amount  of 
base  present  has  been  fully  neutralized.  The  bases  most  favor- 
able to  nitrification  are  lime  and  magnesia  in  the  form  of  car- 
bonates, an  excess  of  which  does  no  harm ;  while  in  the  case 
of  the  carbonates  of  potash  and  soda,  the  amount  must  be 
strictly  limited. 

Conditions  of  Activity. — Dumont  and  Crochetelle  found  that  up  to 
.25  per  cent,  potassic  carbonate  acted  favorably  on  the  process;  which 
was,  however,  completely  stopped  by  as  much  as  .8  per  ct.  War- 
ington has  shown  that  ammonic  carbonate  similarly  prevents  nitrifi- 
cation when  exceeding  about  .37  per  ct.  Ammonia  salts  in  general 
appear  to  be  antagonistic  to  the  transformation  of  nitrites  into  nitrates. 

Aside  from  the  carbonates,  some  neutral  salts  favor  nitrifi- 
cation very  markedly;  while  others  tend  to  depress  it. 
Deherain  found  that  .5  per  cent  of  common  salt  suffices  to  pre- 


SOIL  AND  SUBSOIL.  147 

vent  nitrification  altogether,  while  smaller  amounts  retard  it 
proportionally.  According  to  Dumont  and  Crochetelle,  potas- 
sium chlorid  acts  favorably  up  to  .3  per  cent,  but  at  .8  per 
cent,  suppresses  nitrification.  Earthy  and  alkaline  sul fates,  on 
the  contrary,  seem  to  act  favorably  throughout,  at  least  up  to 
.5  per  cent,  this  is  especially  true  of  gypsum,  which,  according 
to  Pichard,  accelerates  the  process  more  than  any  other  sub- 
stance known.  Taking  the  effect  of  gypsum  as  the  maximum, 
he  found  that,  other  things  being  equal,  the  amounts  of  nitrates 
formed  were  as  shown  in  the  table  below,  the  effect  of  gypsum 
being  taken  as  100: 

Gypsum i  oo 

Sodic  Sulfate 4 7 .9 

Potassic Sulfate 35.8 

Calcic  Carbonate 1 3.3 

Magnesic  Carbonate 12.5 

The  above  estimates  are  markedly  confirmed  by  the  observations  of 
the  writer  in  the  alkali  soils  of  California.  In  these,  nitrates  exist  most 
abundantly  when  the  salts  contained  in  the  soil  are  mainly  sulfates ; 
while  wherever  common  salt  or  sodic  carbonate  are  present  in  con- 
siderable amounts,  the  amounts  of  nitrate  found  are  notably  less.  In 
saline  seashore  lands  nitrates  are  usually  present  in  traces  only.  Wollny 
has  moreover  shown  that  the  nitrates  themselves  exert  a  repressive 
influence  on  nitrification. 

Effects  of  .-I era t ion  and  Reduction.— "While  the  fostering 
effect  of  sulfates  upon  nitrification  is  very  energetic  in  well 
aerated  soils,  they  become  injurious  whenever  by  a  reductive 
process  in  ill-drained  lands,  the  sulfates  are  reduced  to  sulfids. 
Under  such  conditions  the  process  will  in  any  case  be  much  im- 
paired. On  the  other  hand,  the  favoring  effect  of  abundant 
aeration  was  strikingly  shown  in  the  experiment  made  by 
Dcherain.  in  which  a  cubic  meter  of  soil  was  left  unmoved  for 
several  months,  while  a  similar  mass  was  thoroughly  agitated 
once  a  week  during  the  same  time.  The  proportion  of  nitrates 
formed  in  the  latter  case  was  as  70  to  I  formed  in  the  quiescent 
soil  mass.  It  follows  that  the  intensity  of  nitrification  is  essen- 
tially dependent  upon  the  porosity  of  the  soil;  and  that  it  is 
thus  greatly  favored  in  the  pervious  soil-strata  of  the  arid  re- 


148 


SOILS. 


gions.  It  also  follows  that  thorough  and  frequent  tillage  and 
fallowing  greatly  favor  nitrification ;  thus  explaining  one  of 
the  beneficial  results  of  these  operations.  At  the  same  time, 
it  is  true  that  we  may  thus  in  a  short  time  seriously  diminish 
the  reserve  stock  of  nitrogen  contained  in  the  soil  in  the  form 
of  humus-amids;  and  since  nitrates  are  exceedingly  liable  to  be 
lost  from  the  soil  in  several  ways,  such  excessive  nitrification 
is  to  be  avoided. 

Unhuniificd  Organic  Matter  docs  not  Nitrify. — There  can  be 
little  doubt  that  the  formation  of  ammonia  from  the  amido- 
compounds  in  humus  is  also  the  work  of  bacteria;  but  this, 
really  the  initial  phase  of  the  nitrogen-nutrition  of  plants,  has 
not  yet  been  fully  elucidated.  That,  however,  it  is  essentially 
only  the  reacly-formed  humus  and  not  the  unhumified  debris 
of  the  soil  which  participate  in  nitrification  was  shown  by  the 
experiments  of  the  writer,  see  chapter  19. 

Denitrifying  Bacteria. — Among  the  sources  of  loss  of  ni- 
trates in  the  soil  is  the  action  of  denitrifying  bacteria ;  some  of 
which  cause  merely  the  reduction  of  nitrates  to  nitrites  and 
progressively  to  ammonia,  while  others  cause  gaseous  nitrogen 
to  be  given  off  from  nitrites  and  nitrates,  resulting  in  their 
complete  loss  to  the  soil.  \Yhile  there  are  probably  several 
kinds  of  the  latter  class,  the  most  rapidly  effective  is  an  organ- 
ism contained  abundantly  in  fresh  horse  dung,  and  also  on  the 
surface  of  old  straw.  This  can  readily  be  shown  by  subjecting 
a  very  dilute  solution  (1-3  per  cent.)  of  Chile  saltpeter  to  the 
action  of  fresh  horse  dung  in  a  close  flask,  when  nitrogen 
and  carbonic  dioxid  gases  are  evolved, 
and  in  a  few  days  the  nitrate  has  totally 
disappeared.  In  the  course  of  time  this 
power  of  horse-manure  disappears ;  so  that 
"  rotted  manure  "  is  practically  free  from 
it  and  under  proper  conditions  serves  nitri- 
fication so  effectively,  that  in  the  past  it 
FIG.  17— Bacillus  denitri-  has  served  extensively  for  the  production 
of  saltpeter  in  the  "  niter- plantations  "  for 
the  industrial  purposes;  the  material  of  which  was  loose 


SOIL  AND  SUBSOIL.  149 

earth,  marl  and  manure,  kept  moist  and  frequently  forked 
over  for  better  aeration.  Saltpeter  is  similarly  produced  in 
stables,  corroding  the  mortar  of  brick  foundations.  Neverthe- 
less, it  is  necessary  to  avoid  the  use,  either  together  or  at  short 
intervals  apart,  of  Chile  saltpeter  and  fresh  manure;  the  ma- 
nure if  used  first  should  be  allowed  to  remain  at  least  two 
months  in  the  soil  before  saltpeter  is  applied. 

The  reduction  of  nitrates  to  nitrites  and  ammonia  is  brought  about 
by  quite  a  number  of  bacteria,  mostly  anaerobic,  and  such  as  consume 
combined  oxygen  in  their  development.  Thus  the  butyric  ferment, 
which  in  the  absence  of  readily  reducible  compounds  evolves  free  hy- 
drogen, will  in  presence  of  nitrates  reduce  the  latter  to  nitrites,  or  form 
ammonia  by  addition  of  hydrogen  to  nitrogen  just  set  free  by  reduction. 
Such  reductive  processes  of  course  occur  chiefly  in  soils  rich  in  organic 
matter,  or  ill-aerated.  The  ammonia  so  formed,  while  at  first  simply 
combining  with  any  humus  acids  present,  may  in  the  course  of  time  be 
itself  reduced  to  the  amidic  condition,  being  thereby  rendered  relatively 
inert,  until  again  brought  into  action  by  ammonia-forming  bacteria. 

Ammonia-forming  Bacteria. — A  large  number  of  different 
bacteria  appear  to  be  concerned  in  the  formation  of  ammonia 
from  compounds  of  the  albuminoid  group,  (and  probably  from 
humus).  Among  these  is  one  of  the  most  common  in  soils 
(Bacillus  niycoidcs,  root  bacillus),  which  while  forming  am- 
monia carbonate  in  solutions  of  albumen,  is  also  capable  of 
reducing  nitrates  to  nitrites  and  ammonia  in  presence  of  a 
nutritive  solution  of  sugar. 

The  "hay  bacillus"  (  H.  snbtilis},  so  abundantly  developed 
in  ha}'  infusions,  and  one  of  the  most  abundant  in  cultivated 
soils,  has  together  with  P>.  ellenbachensis.  R.  megatherium,  B. 
mycoides,  and  others,  by  some  been  credited  with  important 
action  in  favoring  vegetation;  so  that  a  fairly  pure  culture  of 
I*,  ellenbachensis  has  been  brought  out  commercially  in  Ger- 
many under  the  name  of  "  Alinit."  Rigorous  culture  experi- 
ments made  by  Stutxer  and  others  have,  however,  failed  to 
show  any  general  benefit  from  the  use  of  alinit  in  infecting 
either  land  or  seeds.  Hut  there  is  no  doubt  of  the 

Effects  of  Bacterial  Life  on  Physical  Soil  Conditions. — Tt  is 
apparent  that  all  conditions  favoring  the  life  of  aerobic  (air- 
needing)  bacteria  tend  also  to  produce  the  loose,  porous  state 


SOILS. 


(tilth)  of  the  surface  soil  so  conducive  to  the  welfare  of  cul- 
ture plants,  designated  by  German  agriculturists  as  "  Boden- 

gare."  Whether  or  not  this  con- 
dition is  directly  due  to  bacterial 
processes,  as  is  thought  by  Stut- 
zer  (Landw.  Presse,  1904,  No. 
1 1 )  it  is  assuredly  a  highly  im- 
portant point  to  be  gained,  and 
is  essentially  connected  with  the 
presence  of  humus  in  adequate 
amounts,  which  is  also  a  favor- 
ing condition  of  abundant  bac- 
terial life.  It  seems  that  the 
FIG.  ,8. -Bacillus  subtiiis.  (Woiiny,  after  preference  given  to  the  shallow 

Brefeld.  .  .  r  ,. 

putting-m,  or  even  surface  appli- 
cation of  stable  manure,  existing 
in  Europe,  is  largely  based  upon 
the  marked  effect  upon  the  loose- 
ness of  the  surface  soil,  generally 
credited  to  the  physical  effect  of 
the  manure  substance  itself,  but 
apparently  largely  due  to  the  in- 
tensity of  bacterial  action  thus 
brought  about. 

ROOT-BACTERIA  OR  RHIZOBIA 
OF  LEGUMES. — Among  the  most 
important  bacteria,  agricultur- 
ally, is  that  which  enables  plants 
of  the  leguminous  order — (peas, 
beans,  vetches,  clovers,  lupins, 
etc.), — to  obtain  their  supply  of 
nitrogen  from  the  air  independ- 
ently of  those  contained  in  the 
soil.  The  source  of  nitrogen 
to  plants  was  long  a  disputed 
question  ;  it  was  at  first  supposed 
(  by  cle  Saussure)  that  it  was  ob- 
tained directly  from  the  soil  by 
the  absorption  of  humus ;  but  this  was  disproved,  and  Liebig 
then  contended  that  it  was  derived  directly  from  the  atmos- 


FlG.  19. — Bacteria  producing  ammoniacal 
fermentation  :  A  ,  C.  mycoides  :  B,  B.  stut- 
zeri.  (From  Conn,  Agr.  Bacteriology.) 


FIG.   20. — Bacillus 

Migula.) 


magaterium.        (  From 


SOIL  AND  SUBSOIL,  I5I 

phere  through  the  ammonia  in  rain  water.  This  was  then 
shown  to  be  wholly  inadequate;  and  Boussingault  proved  con- 
clusively that  plants  do  not  take  up  nitrogen  gas  from  the  air. 
This  was  subsequently  denied  by  Ville;  but  investigation  at 
the  Rothamstead  agricultural  station  by  Laxves  and  Gilbert 
definitely  confirmed  Boussingault's  results.  At  the  same  time 
they  also  proved  very  definitely  that  while  grass  and  root  crops 
deplete  the  soil  of  nitrogen,  clover  and  other  leguminous  crops 
leave  in  the  soil  more  nitrogen  than  was  previously  present, 
even  when  the  entire,  itself  highly  nitrogenous,  leguminous 
crop  is  removed  from  the  land.  The  improvement  of  lands 
for  wheat  production  by  rotation  with  clover  had  long  ago 
become  a  practical  maxim ;  but  the  cause  was  not  understood 
until,  in  1888,  Hellriegel  and  \Yilfarth  announced  that  the 
variously-shaped  excrescences  or  tubercles  which  had  long  been 
observed  as  frequently  deforming  the  roots  of  legumes,  are 
caused  by  the  attacks  of  bacilli  capable  of  absorbing  the  free 
nitrogen  of  the  air  and  thus  enabling  the  host-plant  to  acquire 
its  needed  supply  by  absorbing  the  richly  nitrogenous  matter 
thus  accumulated  in  the  excrescences.  The  minute  rod-shaped 
organism  was  named  Bacillus  radicicola  by  Beyerinck;  Rhico- 
biuin  leguminosarum,  by  A.  Frank,  who  has  published  an  ex- 
tensive treatise  on  the  subject.1 

Microscopic  examination  of  the  nodules  shows  their  tissues 
to  contain  partly  motile,  free 
bacteria,  partly  others  ( bacte- 
roids),  which  hive  assumed  a 
quiescent  condition,  and  are 
of  much  greater  dimensions 
than  those  of  the  motile  form. 
These  relatively  thick,  and 
sometimes  forked,  forms,  dif- 
fering somewhat  in  each  of 
the  group  adaptations  men- 
tioned below,  constitute  the 
bulk  of  the  cell-contents  of  the 
nodules,  and  ultimately  serve 

r  ,1  ,     •,  •  r    ,1          i  Vi<;.    21. — Microscopic     section    of     cell     tissue, 

for  the  nutrition  ot  the  host-  fr,,m  anofhlle  ,,f  sjiuarc.p(ic,  ,„,,.  sh,,willsceu. 
plant  with  nitrogen.  When  fiiii-a  with  Rhizobia.* 

1  Uher  die  Filzsymbcose  di-r  I.eguminosfn.  IVrlin.  iSoo. 

2  Original    figure    from    thawing   l>y    ( ).    Ilutk-r.    Asst.    in    Agr.    1  >rp't    L'niv.  of 
California. 


152 


SOILS. 


the  growth  of  the  excrescence  is  completed,  the  swollen,  quies- 
cent bacteroids  gradually  collapse  and  become  depleted  of 
their  nitrogenous  substance;  and  finally  the  apparently  empty 
husk  remains  or  drops  off,  carrying  with  it  the  minute  cocci 
which  in  the  soil  become  active  bacteria  again.  The  nodules 
are  thus  found  mainly  on  the  actively-growing  roots,  and  at 
the  time  when  vegetation  and  assimilation  are  most  active  in 
the  plant.  In  autumn,  or  when  the  plants  are  in  fruit,  the  roots 
may  be  wholly  destitute  of  nodules. 


FIG.  25. — Square-pod  pea. — Tetragonolobus  purpureus.     FIG.  26. — White  Lupin. — I.upinus  albus. 

The  adhesion  of  the  nodules  to  the  roots  is  mostly  very 
loose,  and  their  falling-off  when  the  seedlings  are  carelessly 
transplanted,  doubtless  accounts  for  much  of  the  difficulty 
generally  found  in  transplanting  legumes  when  once  es- 
tablished. 

The  figures  annexed  show  the  various  forms  assumed  by  the 
nodules  in  different  plants,  and  with  them  also  the  correspond- 
ing forms  of  the  bacteroids  of  each.  The  latter,  here  shown 


SOIL  AND  SUBSOIL. 


153 


1 54  SOILS. 

magnified  about  1000  times,  are  taken  from  the  inaugural  dis- 
sertation of  D.  Brock  on  this  subject,  published  at  Leipzig  in 
1891.  It  appears  that  the  forms  of  the  bacteroids  are  quite  as 
much  varied  as  are  those  of  the  nodules  they  form. 

Varieties  of  Forms. — While  these  bacilli  seem  to  be  normally 
present  in  most  soils,  it  seems  to  be  necessary  that  they  should 
adapt  themselves  for  this  symbiosis l  with  each  of  several 
groups  of  the  legumes  in  order  to  exert  their  most  beneficial 
effects.  In  many  soils  there  appears  to  exist  a  "  neutral  form, 
which  requires  about  a  season's  time  or  more  to  adapt  itself 
specially  to  the  several  leguminous  groups  so  that  a  great  ad- 
vantage is  gained  by  infecting  either  the  seeds  or  the  soil  with 
the  forms  already  adapted,  when  no  similar  plant  has  lately 
occupied  the  same  ground.  Thus  the  bacillus  of  the  clover 
root  is  of  little  or  no  benefit  to  beans,  peas  or  alfalfa,  and  the 
root-bacilli  of  each  of  the  latter  are  relatively  ineffectual  when 
used  to  infect  either  of  the  other  groups.  The  same  is  true  of 
the  bacilli  of  lupins  and  of  acacias,  as  applied  to  leguminous 
plants  of  any  other  groups.2 

Mode  of  Infection. — The  infection  is  especially  effectual 
when  applied  to  the  seeds  before  sowing;  and  for  that  purpose 
there  may  be  used  either  the  turbid  water  made  by  stirring  up 
in  it  some  earth  of  a  properly  infected  field,  or  else  water 
charged  with  a  pure  culture  of  the  appropriate  kind,  commer- 
cially known  under  the  name  of  nitragin,  now  manufactured 
for  the  purpose.  Or  else,  the  field  to  be  sown  may  be  infected 
by  spreading  on  it  broadcast,  and  promptly  harrowing  in,  a 
wagon-load  of  earth  per  acre  from  a  properly  infected  field. 
Such  earth  must  not  be  allowed  to  dry,  or  to  be  long  exposed 
to  light. 

Specially  effective  ("virulent")  and  hardy  forms  of  such  bacteria 
have  been  produced  under  artificial  culture  by  Dr.  Geo.  T.  Moore  of 
the  U.  S.  Department  of  Agriculture.  These  cultures  can  be  sent  by 
mail  on  cotton  imbued  with  them,  for  the  infection  of  seeds. 

1  "  Living  together  "  beneficially ;  in  contradistinction  to  parasitism,  which  is 
injurious  to  the  host  plant. 

2  It  is   asserted   by  some   observers  that  the  root  bacilli  producing  differently- 
shaped  excrescences  upon  different  legumes  are  distinct  species  ;  but  this  view  is 
not  sustained  by  the  experiments  of  Nobbe  and   Hiltner,  and  seems  intrinsically 
improbable. 


SOIL  AND  SUBSOIL. 


155 


It  is  very  important  that  the  bacillus  should  be  present  in 
the  earliest  stages  of  the  growth  of  the  seedlings;  otherwise  the 
latter  will  undergo  a  longer  or  shorter  period  of  starvation, 
unless  the  soil  contains,  or  is  furnished  with,  a  sufficiency  of 
available  nitrogen  to  supply  their  immediate  wants.  When 
such  a  supply  is  very  abundant,  the  legume  crop  will  sometimes 
develop  no  nodules  at  all ;  but  the  best  crops  appear  to  be  the 
result  of  a  thorough  infection,  and  abundant  formation  of  the 
excrescences. 

Cultural  Results. — The  marked  results  obtained  in  certain 
soils  by  inoculation  with  the  legume-root  bacillus  are  exempli- 
fied in  the  following  table,  showing  results  of  experiments  by 
J.  F.  Duggar,  at  the  Alabama  Experiment  station.1 

TABLE   SHOWING    IXCKKASE    OF    PRODUCTION'    BY   SOIL   INOCULATION'. 


I'KR  ACRE. 

TOPS. 
Ibs. 

ROOTS. 
Ibs. 

NITR< 

Ibs. 

)GF.N. 

Value. 

Hairy  vetch,  not  inoculated  

194 

3°45 
1  06 
4840 

387 

145= 
266 
1452 

7 
1  06 

4-3 

'437 

?  1.05 

I  vQO 

•65 
2F.25 

do.     do.      inoculated  . 

Crimson  clover  not  inoculated  

do.     do.     inoculated  

Such  marked  increases  from  soil  inocculation  cannot  of 
course  be  expected  in  cases  where  the  soil  has  previously  borne 
leguminous  crops  of  similar  nature  and  therefore  already  con- 
tains the  root  bacteria.  I  Icnce  Duggar  found  no  increase  of 
production  when  inoculating  for  cowpea.  land  that  had  borne 
that  crop  two  years  before  and  already  contained  the  root  bac- 
teria. In  the  arid  region,  where  the  almost  universally  calcare- 
ous soils  usually  bear  a  natural  growth  largely  composed  of 
various  leguminous  plants,  inoculation  is  likely  to  be  less  com- 
monly effective  than  in  the  humid  region  east  of  the  Missis- 
sippi, where  leguminous  plants  are  much  less  generally  present 
in  the  native  flora. 

The  distinctive  agricultural  function  of  supplying  nitrogen 
to  the  soils  on  which  they  grow,  renders  inexcusable  the  per- 
sistence of  some  writers  and  teachers  in  designating  all  forage 
plants  as  "  grasses."  \Yhatever  excuse  there  may  have  been 
for  this  practice  so  long  as  the  nitrogen-gathering  function  of 
the  legumes  was  unknown,  disappears  with  this  discovery,  and 

1  Hull.  Ala.  Exp't  Station,  No.  96.  1898. 


156  SOILS. 

the  misleading  misnomer  should  be  banished  from  agricultural 
publications  and  lectures,  at  the  very  least. 

Other  Nitrogen-Absorbing  Bacteria. — An  increase  in  the 
nitrogen-content  of  some  soils,  aside  from  the  action  of  legu- 
minous root-bacteria,  has  long  been  observed.  As  already 
stated,  this  increase  was  at  first  ascribed  to  certain  green  algae 
often  seen  to  develop  on  the  soil  surface;  but  it  has  now  been 
shown  that  the  nitrogen-gathering  function  belongs  to  at 
least  two  bacteria,  one  of  which  (Clostridium  pastorianum} 
was  discovered  by  Winograclski,  the  other  (Azotobacter 
chroococcum)  by  Beyerinck,  and  has  since  been  farther  in- 
vestigated by  Koch,  Krober,  Gerlach  and  Vogel,  and  last  by 
Lipman  and  Hugo  Fischer.  According  to  the  latter  it  seems 
likely  that  Azotobacter  chroococcum  lives  in  symbiosis  with 
the  green  algae,  all  of  which,  like  the  Azotobacter  itself,  de- 
velop with  special  luxuriance  on  calcareous  soils. 

Lipman  (Rep.  Agr.  Exp't  Station,  New  Jersey,  1903  and  1904) 
describes  as  Azotobacter  vinelandii  a  form  somewhat  different  from  the 
A.  chroococcus,  the  nitrogen-assimilating  power  of  which  he  tested 
quite  elaborately.  He  exposed  to  air  pure  cultures  of  A.  vinelandii  in 
nutritive  solution  containing  the  proper  mineral  ingredients,  and  glucose 
20  grams  per  liter.  100  cub.  centimeters  of  this  solution  was  exposed 
in  flasks  of  respectively  250,  500  and  1000  cc.  content,  therefore  having 
greater  surface  in  the  larger  flasks.  After  ten  days,  the  amounts  of 
nitrogen  fixed  were  found  to  be  respectively  1.67,  3.19  and  7.90  milli- 
grams. When  mannite  solution  was  employed  instead  of  glucose,  a 
similar  fixation  was  observed  ;  and  it  was  also  shown  that  the  presence 
of  combined  nitrogen  in  the  forms  of  nitrates  or  ammonium  salts  dis- 
couraged the  fixation  by  the  bacillus. 

It  was  thus  clearly  proved  that  A.  rinclandii  at  least  does  not  need 
symbiosis  with  algae  to  fix  atmospheric  nitrogen  ;  but  experiments  with 
mixed  cultures  of  the  above  bacillus  and  another  (designated  as  No,  30 
by  Lipman)  proved  that  when  these  two  co-operate  the  absorption  of 
atmospheric  nitrogen  is  nearly  doubled.  As  it  is  probable  that  this  is 
the  case  also  with  other  soil  bacteria,  the  importance  of  this  source  of 
nitrogen  to  plants  is  obvious ;  provided  of  course  that  the  proper  nu- 
tritive ingredients  are  present  in  available  form.  Lipman  shows  that 
among  the  organic  nutrients,  besides  the  sugars,  glycerine  and  the  salts 
of  propionic  and  lactic  acids,  and  probably  also  others  of  the  same 
groups,  can  serve  as  nourishment  to  the  nitrogen-fixing  bacteria. 


SOIL  AND  SUBSOIL.  157 

DISTRIBUTION   OF   THE   HUMUS   WITHIN   THE   SURFACE  SOIL. 

The  uniform  distribution  of  the  humus-contents  of  the  sur- 
face soil,  as  shown  in  sections  of  the  same,  is  by  no  means  easil\ 
accounted  for.  The  roots  from  which  its  substance  is  so  largely 
derived  are  not  so  universally  distributed  as  to  account  for 
it ;  but  least  of  all  can  the  rapid  disappearance  of  the  leaf-fall 
and  other  vegetable  offal  from  the  surface  be  accounted  for 
without  some  outside  agencies.  Of  these,  the  action  of  fun- 
gous vegetation,  and  of  insects  and  earthworms,  are  doubtless 
the  chief  ones. 

Fungi. — \Yhen  we  examine  a  decaying  root,  we  find  radiat- 
ing from  it  a  zone  of  deeper  tint,  as  though  from  a  colored 
solution  penetrating  outward.  Rut  since  under  normal  con- 
ditions humus  is  insoluble,  this  explanation  cannot  stand. 
Microscopic  examination,  however,  reveals  that  the  outside 
limit  of  this  zone  is  also  the  limit  to  which  the  fungous  fibrils 
concerned  in  the  process  extend ;  and  as  these  fibrils  are  much 
more  finely  distributed  and  much  more  numerous  than  the 
roots  of  any  plant,  it  is  natural  that  the  humus  resulting  from 
their  decomposition  should  be  more  evenly  distributed  than 
the  roots  themselves.1 

Such  fungous  growth  is  not,  however,  confined  to  dead  and 
decaying  roots  only.  A  large  number  of  trees  and  shrubs, 
among  them  pines  and  firs,  beeches,  aspen  and  many  others, 
also  the  heaths,  and  woody  plants  associated  with  them,  appear 
to  depend  largely  tor  their  healthy  development,  notably  in 
northern  latitudes,  upon  the  co-operation  ("symbiosis")  of 
fungous  fibrils  that  "  infest  "  their  roots,  enabling  them  to 
assimilate,  indirectly,  the  decaying1  organic  (and  inorganic) 
matter  which  would  otherwise  be  unavailable,  and  at  the  same 
time  converting  that  matter  into  their  own  substance.  Fun- 
gous growths  thus  mediate  both  the  decomposition  and 
rehabilitation  of  the  vegetable  debris. 

The  vegetative  fibrils  (mycelia)  of  several  kinds  of  molds 
are  constantly  present  in  the  soil,  and  while  consuming  the 
dead  tissue  of  the  higher  plants,  spread  their  own  substance 
throughout  the  soil  mass.  The  same  is  true  of  the  subter- 

1  Kosticheff,  Formation  ami  Properties  of  Humus;  in  abstract  T<>ur.  ('hem.  Soc. 
.1891,  p.  61 1. 


158  SOILS. 

ranean  or  "  root "  mycelia  of  the  larger  fungi,  toadstools, 
mushrooms,  which  are  commonly  found  about  dead  stumps 
and  other  deposits  of  decaying  vegetable  and  animal  offai. 
All  these  being  dependent  upon  the  presence  of  air  for  their 
life  functions,  remain  within  such  distance  from  the  surface  as 
will  afford  adequate  aeration ;  the  depth  reached  depending 
upon  the  perviousness^of  the  soil  and  subsoil.  In  the  humid 
region  this  will  usually  be  within  a  foot  of  the  surface,  but  in 
the  arid  may  reach  to  several  feet.  Ultimately  these  organ- 
isms contribute  their  substance  to  the  store  of  humus  in  the 
land. 

On  the  surface  of  moist  soils  we  frequently  find  a  copious  growth  of 
green  fibrils,  which  may  be  either  those  of  algae,  such  as  Oscillaria,  or 
the  early  stages  (prothallia)  of  moss  vegetation.  This  vegetation  has 
been  credited  with  absorption  of  nitrogen  from  the  air,  thus  enriching 
the  soil;  but  later  researches  have  shown  this  effect  to  be  due  to 
symbiotic  bacteria  (see  above  p.  156). 

Animal  Agencies. — Darwin  first  suggested  that  wherever  the 
common  earthworm  (Liunbricus)  finds  the  conditions  of  ex- 
istence, it  exerts  a  most  important  influence  in  the  formation 
of  the  humous  surface-soil  layer;  and  the  limitation  imposed 
upon  these  conditions  by  the  subsoil  has  doubtless  a  great  deal 
to  do  with  the  sharp  demarcation  we  often  find  between  it  and 
the  surface  soil.  Briefly  stated,  the  earthworm  nourishes  itself 
by  swallowing,  successively,  portions  of  the  surrounding  earth, 
digesting  a  part  of  its  organic  matter  and  then  ejecting  the  un- 
digested earth  in  the  form  of  "  casts/'  such  as  may  be  seen  by 
thousands  on  the  surface  of  the  ground  during  or  after  a  rain. 
Darwin  (The  Formation  of  Vegetable  Mold,  1881),  has  cal- 
culated from  actual  observation  that  in  humid  climates  and  in 
a  ground  fairly  stocked  with  these  worms,  the  soil  thus  brought 
up  may  amount  to  from  one-tenth  to  two-tenths  of  an  inch 
annually  over  the  entire  surface;  so  that  in  half  a  century  the 
entire  surface  foot  might  have  been  thus  worked  over.  Aside 
from  the  mechanical  effect  thus  achieved  in  loosening  the  soil, 
and  the  access  of  air  and  water  permitted  by  their  burrows,  the 
chemical  effects  resulting  from  their  digestive  process,  and  the 
final  return  of  their  own  substance  to  the  soil  mass;  also  their 


SOIL  AND  SUBSOIL. 


159 


habit  of  drawing  after  themselves  into  their  burrows  leafstalks, 
blades  of  grass  and  other  vegetable  remains,  renders  their  work 
of  no  mean  importance  both  from  the  physical  and  chemical 
point  of  view.  The  uniformity,  lack  of  structure  and  loose 
texture  of  the  surface  soil,  especially  of  forests,  as  compared 
with  subsoil  layers  of  corresponding  thickness,  is  doubtless 
largely  due  to  the  earthworms'  \vork.  It  has  frequently  been 
observed  that  when  an  unusual  overflow  has  drowned  out  the 
earthworm  population  of  a  considerable  area,  the  surface  soil 
layer  remains  compacted,  and  vegetation  languishes,  until  new 
immigration  has  restocked  the  soil  with  them.  Again,  the 
humus  formed  under  their  influence  is  always  neutral,  never 
acid. 

Wollny  (Forsch,  Agr.,  1890^.382),  has  shown  by  direct  experimental 
cultures  in  boxes,  with  and  without  earthworms,  surprising  differences 
between  the  cultural  results  obtained,  and  this  has  been  fully  confirmed 
by  the  subsequent  researches  of  Djemil  (Her.  Physiol.  Lab.  Vers. 
Halle,  1898).  In  Wollny's  experiments,  the  ratio  of  higher  production 
in  the  presence  of  the  worms,  varied  all  the  way  from  2.6  per  cent  in 
the  case  of  oats,  93.9  in  that  of  rye,  135.9  m  tna*  °f  potatoes,  300  in 
that  of  the  field  pea,  and  140  in  that  of  the  vetch,  to  733  per  cent  in 
the  case  of  rape.  Wollny  attributes  these  favorable  effects  in  the  main 
to  the  increased  looseness,  and  perviousness  of  the  soil  to  air,  and 
diminished  water-holding  power.  DjemiPs  results  all  point  in  the  same 
direction ;  and  he  shows,  moreover,  that  the  allegation  that  the  roots 
penetrate  more  deeply  in  the  presence  of  the  worms  by  following  their 
burrows,  is  unfounded,  the  descending  roots  often  passing  close  to  and 
outside  of  these. 

The  work  of  earthworms  is  especially  effective  in  loamy  soils 
and  in  the  humid  regions.  In  the  arid  region,  and  in  sandy 
soils  generally,  the  life-conditions  are  unfavorable  to  the 
worm,  and  the  perviousness  elsewhere  brought  about  by  its 
labors  already  exists  naturally  in  most  cases.  Tt  is  stated  by 
V..  T.  Seton  (  Century  Mag.  for  June,  i<)O4)  that  the  earth- 
•\vorin  is  practically  non-existent  in  the  arid  region  between  the 
Rocky  Mountains  and  the  immediate  Pacific  coast,  from  Mani- 
toba to  Texas.  In  the  Pacific  coast  region,  however,  they  are 
abundant,  and  do  their  work  effectttallv. 


160  SOILS. 

Insects  of  various  kinds  are  also  instrumental  in  producing, 
not  only  the  uniform  distribution  of  humus  in  the  surface  soil, 
but  also  the  looseness  of  texture  which  we  see  in  forest  soils 
especially.  Ants,  wasps,  many  kinds  of  beetles,  crickets,  and 
particularly  the  larvae  of  these,  and  of  other  burrowing  crea- 
tures, often  form  considerable  accumulations,  due  directly  both 
to  their  mechanical  activity,  and  to  their  excrements. 

The  work  of  ants  is  in  some  regions  on  so  large  a  scale  as  to 
attract  the  attention  of  the  most  casual  observer.  Especially 
is  this  the  case  in  portions  of  the  arid  region,  from  Texas  to 
Montana,  where  at  times  large  areas  are  so  thickly  studded  with 
hills  from  three  to  twelve  feet  in  diameter,  and  one  to  two  feet 
high,  that  it  is  difficult  to  pass  without  being  ^attacked  by  the 
insects.  The  "  mounds "  studding  a  large  portion  of  the 
prairie  country  of  Louisiana  seem  also  to  be  clue  to  the  work 
of  ants,  although  not  inhabited  at  present. 

Larger  burrowing  animals  also  assist  in  the  task  of  mixing 
uniformly  the  surface  soils,  and  aiding  root-penetration,  as  well 
as,  in  many  cases,  the  conservation  of  moisture.  Seton  (loc. 
cit.)  even  claims  that  the  pocket  gophers  (Thomomys)  in  a 
great  degree  replace  the  activity  of  the  earthworms  in  the  arid 
region,  where  they,  together  with  the  voles  (commonly  known 
there  as  field  mice),  exist  in  great  numbers.  Of  course  the 
work  of  these  animals,  as  well  as  that  of  the  prairie  dogs, 
ground  squirrels,  badgers,  etc.,  is  incompatible  with  cultiva- 
tion. But  the  effects  of  their  burrows  on  the  native  vegeta- 
tion, and  the  indications  they  give  of  the  nature  of  the  subsoil, 
are  eminently  useful  to  the  land-seeker. 

Thus  in  the  rolling  sediment-lands  of  the  Great  Bend  of  the  Columbia, 
the  observer  is  surprised  to  see  the  "  giant  rye  grass,"  usually  at  home 
in  the  moist  lowlands,  growing  preferably  on  the  crests  of  the  ridges 
bordering  the  horizon.  Examination  shows  that  this  is  due  to  the 
burrowing  of  badgers,  whereby  the  roots  of  the  grass  are  enabled  to 
reach  moisture  at  all  times,  even  in  that  extremely  arid  region. 


CHAPTER  X. 

SOIL  AND  SUBSOIL  (Continued) 

THKIR   RELATIONS  TO  VEGETATION. 

Physical  Effects  of  the  Percolation  of  Surface  Waters. — 
The  muddy  water  formed  by  the  beating  of  rains  on  the  soil 
surface  will,  in  penetrating  the  soil,  carry  with  it  the  diffused 
colloidal  clay  to  a  certain  depth  into  the  subsoil.  \Ye  should 
therefore  expect  that  as  a  rule  every  subsoil  will  be  more 
clayey  than  its  surface  soil ;  and  this  is  found  to  be  almost  uni- 
versally the  case  in  the  humid  region.  Subsoils  are  therefore 
almost  always  less  percious  and  more  retentive  of  moisture,  as 
well  as  of  plant-food  substances  in  solution,  than  their  surface 
soils,  unless  these  are  very  rich  in  humus;  and  as  the  finest 
particles  are  usually  those  richest  in  available  plant-food,  it 
follows  that  subsoils  will  as  a  rule  be  found  to  contain  larger 
supplies  of  the  latter  than  the  surface  soil.  Common  experi- 
ence as  well  as  comparative  analysis  confirm  both  of  these  in- 
ferences so  thoroughly,  that  it  becomes  unnecessary  to  adduce 
examples  in  this  place. 

On  the  other  hand,  the  reverse,  upward  movement  of  moist- 
ure caused  by  surface  evaporation  tends  constantly  to  bring 
any  soluble  sails  contained  in  the  soil  mass  nearer  to  the  sur- 
face, thus  increasing  the  stock  of  easily  available  plant-food  in 
the  surface  soil.  In  extreme  cases,  especially  in  the  arid 
region,  this  accumulation  <>|  salts  may  become  excessive,  and 
seriously  injurious  to  plant  growth.  (Sec  "Alkali  Soils, 
chapters  21,  22. ) 

Chemical  effects  of  U'atcr-Pcrcolation. — The  accumulation 
of  plant-food  in  the  subsoil  is  not,  however,  due  only  to  the 
mechanically-carried  particles,  but  also  to  the  ingredients 
carried  in  solution  from  the  surface  soil  and  redeposited  in  the 
more  retentive  subsoils.  Especially  is  this  true  of  /;';//('  car- 
bonate, which  is  dissolved  by  the  carbonic  acid  formed  chiefly 
II  i  o  i 


!62  SOILS. 

within  the  humic  surface  soil,  and  is  often  carried  off  in 
amounts  sufficient  to  obstruct  drain  tiles  by  its  deposition  in 
contact  with  air  (see  chapt.  3).  In  the  case  of  moderate  rains, 
however,  it  is  carried  no  farther  than  the  subsoil,  and  is  there 
redeposited,  in  consequence  of  the  penetration  of  air,  following 
the  water,  and  causing  the  carbonic  gas  to  diffuse  upward; 
thus  leaving  the  lime  carbonate  behind.  In  the  majority  of 
cases  this  results  simply  in  a  gradual  enriching  of  the  subsoil  in 
this  substance;  while  the  surface  soil  may  become  so  depleted 
as  to  require  its  artificial  replacement  by  liming  or  marling. 
The  same  general  process  occurs  to  a  less  extent,  in  the  case  of 
magnesia. 

Calcareous  Subsoils — The  fact  that  subsoils  are  more  cal- 
careous than  the  corresponding  surface  soils  is  often  of  great 
practical  importance,  in  enabling  the  farmer  to  enrich  his  de- 
pleted surface  soil  in  lime  by  subsoil  plowing.  The  accumula- 
tion of  lime  carbonate  in  the  subsoil  also  tends  in  a  measure  to 
offset  the  extreme  heaviness  sometimes  resulting  from  the  ac- 
cumulation of  clay. 

Calcareous  Subsoils  and  Hardpans. — When  soils  are  very 
rich  in  lime,  and  rains  occur  in  limited  showers  rather  than  con- 
tinuously, the  lime  carbonate  dissolved  from  the  surface  soil 
may  accumulate  in  the  subsoil  so  as  to  either  form  calcareous 
"  hardpan  "  by  the  cementing  of  the  subsoil  mass;  or  it  may 
accumulate  and  partly  crystallize  around  certain  centers  and 
thus  form  white  concretions,  known  to  farmers  as  "  white 
gravel."  The  latter  is  the  form  usually  assumed  in  the  re- 
gions of  summer  rains ;  while  in  the  arid  regions  the  deficient 
rainfall  causes  this  substance  to  accumulate,  and  calcareous 
hardpan  to  form,  at  definite  depths  depending  upon  the  maxi- 
mum penetration  of  the  annual  rainfall ;  sometimes  in  crystal- 
line masses  of  veritable  limestone  ("kankar"  of  India),  or 
sometimes  merely  as  crystalline  incrustations  loosely  cementing 
the  subsoil. 

"Rawness"  of  Subsoils  in  Humid  Climates. — From  the 
greater  compactness  of  the  subsoil  which  is  almost  universal  in 
the  humid  regions,  the  absence  of  humus  and  of  the  resulting 
formation  of  carbonic  and  humic  acids,  it  follows  that  its 
minerals  are  less  subject  to  the  weathering  process  than  are 


SOIL  AND  SUBSOIL.  163 

those  of  the  surface  soil.  In  the  farmer's  parlance,  the  sub- 
soil is  "  raw  "  as  compared  with  the  surface  soil;  it  is  not  so 
suitable  for  plant-nutrition,  and  therefore  must  not  be  brought 

.  to  the  surface  to  form  the  seed-bed,  or  be  incorporated  with 
the  surface  soil  to  any  considerable  extent  at  any  one  time,  if 
crop-nutrition  is  to  be  normal.  It  is  only  in  the  course  of  time, 
by  exposure  to  atmospheric  action  as  well  as  to  that  of  the 
humus,  and  of  plant  roots,  that  it  becomes  properly  adapted  to 
perform  the  functions  of  the  surface  soil. 

Soils  and  Subsoils  in  the  Arid  Region. — But  however  pro- 
nounced and  important  are  these  distinctions  and  differences  in 
the  humid  region,  they  are  found  to  be  profoundly  modified  in 
the  arid;  where,  as  before  stated,  the  formation  of  colloidal 

*  clay  is  very  much  diminished,  so  that  most  soils  formed  under 
arid  conditions  are  of  a  sandy  or  pulverulent  type.  There  is 
then  little  or  no  clay  to  be  washed  down  into  the  subsoil,  hence 
there  is  no  compacting  of  the  latter;  the  air  consequently  cir- 
culates freely  down  to  the  depth  of  many  feet. 

Thus  one  of  the  most  important  distinctions  between  soil 
and  subsoil  is  to  a  great  extent  practically  non-existent  in  the 
arid  region,  at  least  within  the  depths  to  which  tillage  can  be 
made  to  reach;  so  that  the  limitations  attached  to  subsoil-plow- 
ing in  the  countries  of  summer  rains  do  not  apply  to  the 
characteristic  soils  of  the  arid  regions. 

Kven  the  distinction  in  regard  to  humus  is  here  largely  ob- 
literated by  the  circumstance,  already  alluded  to,  that  most  of 
that  substance  must,  in  the  arid  regions,  he  derived  from  the 
decay  ot  roots,  which  moreover  reach  to  much  greater  depth  in 
these  soils.  Hence  even  in  the  uplands  of  the  arid  region  it  is 
common  to  find  no  change  of  tint  from  the  surface  down  to 
three  feet,  and  even  move-.  This,  like  the  free  circulation  of  the 
air  in  consequence  ot  porosity,  tends  to  render  the  distinction 
of  soil  and  subsoil  practically  useless;  since  it  disposes  of  the 
objection  to  "  subsoiling  "  based  upon  the  inert  condition  of  the 
subsoil,  which  in  humid  climates  so  effectually  interferes  with 
the  welfare  of  crops  unless  subsoiling  is  restricted  to  a  fraction 
of  an  inch  at  a  time. 

These  fundamental  differences  in  the  soils  of  the  two  regions 
are  illustrated  schematically  in  the  subjoined  diagram,  which 
shows  on  the  left  the  contrast  between  clav  or  clav  loam  soils. 


164  SOILS. 

in  which  the  depth  of  the  surface  soil-sample  to  be  taken  is 
prescribed  as  nine  inches  by  the  rules  of  the  Association  of  Am. 
Official  Chemists  (in  the  writer's  experience  it  is  more  nearly 
six  inches  as  a  rule).  Alongside  of  the  Eastern  soil  thus 
characterized  is  placed  a  typical  "  adobe  "  soil  from  the  grounds 
of  the  California  Experiment  station,  of  which  a  sample  show- 
ing uniform  blackness  to  three  feet  depth  was  exhibited  at  the 
World's  Fair  at  Chicago  in  1893.  At  the  right  is  a  profile  of 
the  noted  hop  soil  on  the  bench  lands  of  the  Russian  river,  Cal., 
in  which  the  humus-content  was  determined  down  to  twelve 
feet,  the  humus-percentage  being  .44%  at  that  depth  against 
1.21%  in  the  surface  foot  (see  chapt.  8,  p.  139).  In  this  and 
similar  soils  the  roots  of  hops  reach  down  to  as  much  as 
fourteen  feet  without  much  lateral  expansion ;  as  shown  in  plate 
No.  31  of  this  chapter.  Similar  conditions  prevail  in  the  sandy 
uplands,  as,  e.  g.,  in  the  wheat  lands  of  Stanislaus  county,  Cal., 
mentioned  above. 

Taking  the  clay  soils  as  a  fair  type  for  comparison,  it  would 
seem  that  the  farmer  in  the  arid  region  owns  from  three  to  four 
farms,  one  above  another,  as  compared  with  the  same  acreage 
in  the  Eastern  states. 

Subsoils  and  Deep-plowing  in  the  Arid  Region. — Up  to  the 
present  time  this  advantage  is  but  little  appreciated  and  acted 
upon  by  the  farmers  of  the  arid  region.  They  still  instinctively 
cling  to  the  practice  taught  them  by  their  fathers,  and  which  is 
still  promulgated  as  the  only  correct  practice,  in  most  books  on 
agriculture.  There  are  of  course  in  the  arid  as  well  as  in  the 
humid  region,  cases  in  which  deep  plowing  is  inadvisable ;  viz, 
that  of  marsh  or  swamp  lands,  as  well  as  sometimes  in  very 
sandy,  porous  soils,  the  cultural  value  of  which  often  depends 
essentially  upon  the  presence  of  a  somewhat  consolidated,  and 
more  retentive  subsoil,  which  should  not  be  broken  up.  But  in 
most  soils  not  of  extreme  physical  character,  it  is  in  the  arid 
region  not  only  permissible,  but  eminently  advisable  to  plow, 
for  preparation,  as  deeply  as  circumstances  permit,  in  order  to 
facilitate  the  penetration  of  the  roots  beyond  the  reach  of  harm 
from  the  summer's  drought ;  while  for  the  same  reason,  subse- 
quent cultivation  should  be  to  a  moderate  depth  only,  for  the 
better  conservation  of  moisture,  and  the  formation  of  a  pro- 
tective surface  mulch  (see  chapter  13). 


SOIL  AND  SUBSOIL. 


TYPES  OF  CALIFORNIA  SOILS. 


I'*.?-  %  &^tt?\$\ 
v;:'>^v^0;*^^>> 

^Jv.^^v<^?4) 


. .\f r/v  r  s 

|A*VV  • 
M>v>>?  »M» 

IV^^.OvVV. 


-i.V 


ISS 

yi^si^ii 


«B»3Ea^S^ 

ifiSisia  o>.a^>fin.v 


FIG.  27. — Soil  Profiles  illustrating  differences  in  Soils  of  Humid  and  Arid  Region. 


j66  SOILS. 

It  must  not  l?e  forgotten  that  there  are  in  the  lowlands  of 
the  arid  region  (river  swamps  or  tules,  seacoast  marshes,  etc.,) 
soils  in  which  surface  soil  and  subsoil  are  differentiated  as  fully 
as  in  the  humid  countries ;  at  least  so  long  as  they  have  not  been 
fully  drained  for  a  considerable  length  of  time.  In  swamp 
areas  that  have  been  elevated  above  the  reach  of  overflow  or 
shallow  bottom-water  by  geological  agencies,  even  the  heavy 
swamp  clays  are  fully  aerated  down  to  great  depths,  and  roots 
penetrate  accordingly. 

Examples  of  Plant-growth  on  Arid  Subsoils. — The  fact  that 
in  the  arid  region  the  surface-soil  conditions  reach  to  so  much 
greater  depths  than  in  the  East  and  in  Europe,  is  so  important 
for  farming  practice  in  that  region  that  experimental  evidence 
of  the  same  should  not  be  withheld.  Of  such,  some  cases  well 
established  as  typical  of  California  experience  are  therefore 
cited. 

It  is  well  known  that  in  the  Sierra  Nevada  of  California  the  placer 
mines  of  the  Foothills,  worked  in  the  early  times,  have  long  disappeared 
from  sight,  having  been  quickly  covered  by  a  growth  of  the  bull  pine 
(P.  ponderosa}.  Much  of  this  timber  growth  has  for  a  number  of 
years  past  been  of  sufficient  size  to  be  used  for  timbering  in  mines,  and 
a  second  young  forest  is  springing  up  on  what  was  originally  the  red 
earth  of  the  placer  mines,  which  appears  to  the  eye  as  hopelessly 
barren  as  the  sands  of  the  desert.  In  this  same  red  sandy  earth  not 
unfrequently  cellars  and  house  foundations  are  dug,  and  the  material 
removed,  even  to  the  depth  of  eight  feet,  is  fearlessly  put  on  the  garden 
and  there  serves  as  a  new  soil,  on  which  vegetables  and  small  fruits 
grow,  the  first  year,  as  well  as  ever.  In  preparing  such  land  for  irrigation 
by  leveling  or  terracing  no  heed  is  taken  of  the  surface  soil  as  against 
the  subsoil,  even  where  the  latter  must  be  removed  to  the  depth  of 
several  feet,  so  long  as  a  sufficient  depth  of  soil  material  remains  above 
the  bedrock. 

The  same  is  generally  true  of  the  benchlands ;  the  irrigator  levels, 
slopes  or  terraces  his  land  for  irrigation  with  no  thought  of  discrimina- 
tion between  soil  and  subsoil,  and  the  cultural  result  as  a  rule  justifies 
his  apparent  carelessness.  It  is  only  where  from  special  causes  a  con- 
solidated or  hardpan  subsoil  is  brought  to  the  surface,  that  the  land 
when  leveled  shows  "  spotted  "  crops.  Such  is  the  case  in  some  of  the 
"hog-wallow"  areas  of  the  San  Joaquin  valley  of  California,  and  in 


SOIL  AND  SUBSOIL.  167 

some  cases  where  by  long  cultivation  and  plowing  to  the  same  depth,  a 
compact  soil-layer  or  plowsole  has  been  formed,  and  the  land  is  then 
leveled  for  the  introduction  of  irrigation.  In  these  cases  a  section  of 
the  soil  mass  will  usually  show  a  marked  difference  in  color  and  texture. 
But,  as  a  rule,  in  taking  soil  samples,  no  noticeable  difference  can  be 
perceived  between  the  first  and  the  second,  and  oftentimes  as  far  down 
as  the  third  and  fourth  foot.  The  extraordinary  root-peneti'ation  of 
trees,  shrubs  and  taprooted  herbs,  whose  fibrous  feeding-roots  are  found 
deep  in  the  subsoil  and  are  sometimes  wholly  absent  from  the  surface 
soil,  fully  corroborate  the  conclusion  reached  by  the  eye.  The  roots 
of  grape  vines  have  been  found  by  the  writer  at  the  deptli  of  twenty- 
two  feet  below  the  surface,  in  a  gravelly  clay  loam  varying  but  little  the 
entire  distance.  In  a  similarly  uniform  and  pervious  material,  the 
loess  of  Nebraska,  Aughey1  reports  the  roots  of  the  native  Shepherdia 
to  have  been  found  at  the  depth  of  fifty  feet. 

Resistance  to  Drought.— These  peculiarities  of  the  soils  of 
the  arid  region  explain  without  any  resort  to  violent  hypo- 
theses, the  fact  tint  many  culture  plants  which  in  the  regions  of 
summer  rains  are  found  to  he  dependent  upon  frequent  and 
abundant  rainfall,  will  in  California,  and  in  the  country  west  of 
the  Rocky  Mountains  generally,  thrive  and  complete  their 
growth  and  fruiting  during  periods  of  four  to  six  months  of 
practically  absolute  cessation  of  rainfall;  when  east  of  the 
Mississippi  a  similar  cessation  for  as  many  t^'ccks  will  ruin 
the  crops,  if  not  kill  the  plants.  In  continental  Kurope.  in 
1892,  a  six  weeks'  drought  caused  almost  all  the  fruit  crops  to 
drop  from  the  trees,  and  many  trees  failed  to  revive  the  next 
season;  while  at  the  very  same  time,  the  same  deciduous  fruits 
gave  a  bountiful  crop  in  California,  during  the  prevalence  of 
the  usual  live  or  six  months'  drought.  This  was  without  irri- 
gation, or  any  aid  beyond  careful  and  thorough  surface  til- 
lage following  the  cessation  of  rains  in  April  or  May,  so  as  to 
leave  the  soil  to  the  depth  of  live  or  six  inches  in  a  condition 
ot  looseness  perfectly  adapted  to  the  prevention  of  evaporation 
from  the  moist  subsoil,  and  of  the  conduction  of  the  excessive 
heat  of  the  summer  sun.  This  surface  mulch  will  contain 
practically  no  feeding-roots,  the  paralysis  or  death  of  which 
by  heat  and  drought  would  influence  sensibly  the  welfare  of 
the  growing  plant. 

1  See  Merril1,  Rocks  and  Rockweathering. 


1 68 


SOILS. 


Root-system  in  the  Humid  Region. — It  is  quite  otherwise 
where  a  dense  subsoil  not  only  obstructs  mechanically  the  deep 
penetration  of  any  but  the  strongest  roots,  but  at  the  same 
time  is  itself  too  inert  to  provide  sufficiently  abundant  nourish- 
ment apart  from  the  surface  soil,  which  is  there  the  portion  con- 
taining, alongside  of  humus,  the  bulk  of  the  available  plant- 
food,  and  in  which  alone  the  processes  of  absorption  and  nu- 
trition find  the  proper  conditions;  such  as  access  of  air  and  the 


FIG.  28.— Root  of  an  Lastern  (Wisconsin)  Fruit  Tree.   (Photograph  by  Prof  F.  H.  King.) 

ready  and  minute  penetration  of  even  the  most  delicate  rootlets 
and  root-hairs.  The  largest  and  most  active  portion  of  the 
root-system  being  thus  accumulated  in  the  surface  soil,  it  fol- 
lows that  unless  the  latter  is  constantly  kept  in  a  fair  condition 
of  moistness,  the  plant  must  suffer  material  injury  very  quickly ; 
hence  the  often  fatal  effects  of  even  a  few  weeks'  drought. 
The  same  occurs  in  the  arid  region  when  often-repeated 
shallow'  plowing  has  resulted  in  the  formation  of  a  "  plow- 
sole  "  which  prevents  the  deep  penetration  cf  roots;  when  a 


SOIL  AND  SUBSOIL. 


169 


hot  "  norther  "  will  often  in  a  short  time  not  only  dry  the 
plowed  soil,  but  will  heat  it  to  such  extent  as  to  actually  bake 
the  roots  it  harbors.  Under  the  same  weather-conditions  an 
adjoining  field,  properly  plowed,  may  almost  wholly  escape 
injury. 

Comparison   of  root  development   in    tlie  arid  and  humid 
regions. — Figures  28,  29  given  here  show  the  differences  as 


KJ...  i •).  —  Prune  Tree  on  Peach  Root,  at  Niles,  Cal. 

actually  seen  in  the  case  of  fruit  trees  as  grown  in  \Yisconsin 
and  California,  respectively,  both  in  the  absence  of  artificial 
water-supply. 

Adaptation  of  humid  species  to  arid  conditions. — Figures, 
in  Xo.  ^o.  show  the  mot  systems  respectively  of  the  riverside 
grape  I  1'itis  riparia)  as  grown  in  the  Mississippi  Valley  states, 
and  the  natural  development  as  found  in  the  Rock  grape  of 


SOILS. 


Missouri  and  also  in  the  wild  grape  vine  of  California.  It  will 
be  noted  at  once  that  the  latter  directs  its  cord-like  roots  almost 
vertically  from  the  first,  until  it  reaches  a  depth  varying  from 
12  to  1 8  inches,  where  it  begins  to  branch  more  freely,  but  still 
with  a  strong  dowmvard  tendency  in  all.  The  roots  of  the 
riverside  grape,  on  the  contrary,  tend  to  spread  almost  hori- 
zontally, branching  freely  at  the  depth  of  a  few  inches  and 


FIG.  30.— Root  Growth  of  Resistant  Grape  Vines. 

manifestly  deriving  its  supply  both  of  plant-food  and  moisture 
mainly  from  the  surface  soil.  It  is  curious  to  observe  the 
behavior  of  this  vine  when  cuttings  are  planted  in  California 
vineyards  as  a  resistant  grafting-stock.  Its  first  roots  are 
sent  out  horizontally,  very  much  as  is  its  habit  in  the  East,  so 
long  as  the  soil  moisture  is  maintained  near  the  surface.  But 
as  the  season  advances,  the  more  superficial  rootlets  are  first 
thrown  out  of  action  by  the  advancing  dryness  and  heat  of  the 
surface  soil,  and  many  finally  die  the  first  year. 


SOIL  AND  SUBSOIL. 


171 


Not  unfrequently  the  entire  root  system  developed  by  the  up- 
permost bud  perishes;  but  usually  its  main  roots  soon  begin  to 
recede  from  the  threatening  drought  and  heat  of  the  surface, 
curving,  or  branching  downward  in  the  direction  of  the  moist- 
ure supply,  and  without  detriment  to  their  nutrition  because  of 
the  practical  identity  of  the  surface  soil  and  subsoil.  As  the 
portions  of  the  roots  near  the  surface  thicken  and  mature, 
their  corky  rind  soon  prevents  their  being  injured  by  the  arid 
conditions  to  which  they  are  subjected;  while  the  root-ends, 
finding  congenial  conditions  of  nutriment  and  aeration  in  the 
moist  depths,  develop  without  difficulty  as  they  would  in  their 
humid  home.  Practically  the  same  process  of  adaptation  takes 
place  in  every  one  of  the  trees,  shrubs,  or  perennials  belonging 
to  the  humid  climates,  until  their  root  system  has  assumed 
nearly  the  habit  of  the  corresponding  native  vegetation. 

The  photograph  of  the  roots  of  a  hop  plant,  grown  on  bench 
lands  of  the  Sacramento  river,  shows  the  roots  extending  to  8 
feet  depth,  but  where  broken  off  the  main  root  is  still  nearly 
two  millimeters  in  thickness,  proving  that  it  penetrated  at  least 
two  feet  beyond  the  depth  shown  in  figure  31. 

In  the  case  of  native  annuals,  either  the  duration  of  their 
vegetation  is  extremely  short,  ending  with  or  shortly  after  the 
cessation  of  rains;  or  else  their  tap  roots  descend  so  low,  and 
the  nutritive  rootlets  are  developed  at  such  depth,  as  to  be  be- 
yond reach  of  the  summer's  heat  and  drought.  For  while  it  is 
true  that  rootlets  immersed  in  air-dry  soil  may  absorb  plant- 
food,  this  absorption  is  very  slow  and  can  only  be  auxiliary  to 
the  main  root  system  which,  instead  of  terminating  in  the  sur- 
face soil  as  in  the  humid  region,  will  be  found  to  begin  to 
branch  off  at  depths  of  15  and  iS  inches,  and  may  then  in  sandy 
lands  descend  to  from  4  to  7  feet  even  in  the  case  of  annual 
fibrous-rooted  plants  like  wheat  and  barley.1  In  the  case  of 
maize  the  roots  of  a  late-planted  crop  may  sometimes  be  found 
descending  along  the  walls  of  the  sun-cracks  in  heavy  clay  land 

1  Shaler  (Origin  and  X.itun-  of  Soils;  uth  Kept.  I".  S.  Ceol.  Survey.  P.  31  I ) 
s;iys  •  "  Annual  plants  cannot  in  their  l>rief  period  of  growth  push  their  roots  more 
than  six  to  twelve  inches  l>elo\v  their  root-crowns  " — a  generalization  measurably 
true  for  the  humid  region  only.  According  to  F.  J.  Alway,  the  root>  of  cereals 
penetrate  to  5-7  feet  in  Saskatchewan,  also. 


172 


SOILS. 


FIG.  31.— Hop  Root  from  Sacramento  Beach-land. 


SOIL  AND  SUBSOIL. 


173 


poorly  cultivated ;  and  it  frequently  matures  a  crop  without  the 
aid  of  a  single  shower  after  planting.  See  figures  33,  34. 

The  annexed  plate  (No.  32)  shows  the  main  roots  ,of  two 
native  perennial  weeds  of  California,  the  goosefoot  (Cheno- 
podium  calif  ornicum)  and  the  figwort  (Scrophularia  cali- 
fornica),  common  on  the  lower  slopes  of  the  coast  ranges.  The 
soil  was  a  heavy  clay  loam  or  "  black  adobe  "  resulting  from 
the  weathering  of  the  clay  shale  bedrock,  fragments  of  which 
are  so  abundantly  intermixed  with  the  substrata  that  excava- 
tion of  the  roots  became  very  difficult.  Yet  the  main  root  of 
the  goosefoot  went  down  below  the  depth  of  eleven  feet. 

The  main  root  of  the  figwort,  also,  was  followed  below  the 
depth  of  ten  feet  without  reaching  the  extreme  end.  This 
proves  clearly  that  the  great  penetration  of  the  goosefoot  was 
not,  as  might  be  supposed,  due  to  its  bulbous  root.  Yet  such 
thickening  of  the  root  just  below  the  crown  is  a  rather  common 
feature  in  arid-region  plants,  and  can  here  be  noted  even  in  the 
figwort,  within  whose  botanical  relationship  bulbous  roots  are 
almost  unknown. 

Any  one  accustomed  to  the  cornfields  of  the  Middle  West, 
where  in  the  after-cultivation  of  maize  it  is  necessary  to  re- 
strict very  carefully  the  depth  of  tillage  to  avoid  bringing  up  a 
mat  of  white,  fibrous  roots,  will  be  at  once  impressed  with  the 
remarkable  adaptability  of  maize  to  different  climatic  condi- 
tions, as  exhibited  in  such  cases  and  shown  in  figures  33,  34. 
In  southern  California,  in  the  deep  mesa  or  bench  soils,  corn 
stalks  so  tall  that  a  man  standing  on  horseback  can  barely  reach 
the  tassel,  and  with  two  or  three  large  ears,  are  quite  com- 
monly grown  under  similar  rainfall-conditions. 

Importance  of  proper  Substrata  in  the  Arid  Region. — The 
paramount  need  of  deep  penetration  of  roots  in  the  arid  region 
renders  the  substrata  below  the  range  of  what  is  usually  under- 
stood by  subsoil  in  the  humid  climates,  of  exceptional  import- 
ance. A  good  farmer  anywhere  will  examine  the  subsoil  to 
the  depth  of  two  feet  before  investing  in  land:  but  more  than 
this  is  necessary  in  the  arid  region,  where  the  surface  soil  is 
often  almost  thrown  out  of  action  during  the  greater  part  of 
the  growing  season,  while  the  needful  moisture  and  nourish- 
ment must  be  whollv  drawn  from  the  subsoil  and  substrata; 


1/4 


SOILS. 


SOIL  AND  SUBSOIL. 


175 


FIG.  33. — Kentucky  M.ii/.e,  grown  in  re-pi  m  »f  Summer  Kains.      i  Pli<>u>.;ra|)hy  Iiy   A.  M     1'cier.) 


SOILS. 


FIG.  34.— California  Maize,  Grown  Without  Rain  or  Irrigation. 


bOlL  AND  SUBSOIL.  177 

an  examination  of  which  should  therefore  precede  every  pur- 
chase of  land,  or  planting  of  crops. 

Such  examinations  are  most  quickly  made  by  means  of  a  probe  con- 
sisting of  a  pointed,  square  steel  rod  five  or  six  feet  long,  provided  at 
one  end  with  a  loop  for  the  insertion  of  a  cross  handle  like  that  of  a 
carpenter's  auger.  The  handle  being  grasped  with  both  hands,  the 
probe  is  forced  into  the  soil  with  a  slight  reciprocating  motion,  by  the 
weight  of  the  operator;  who  socn  learns  how  to  interpret  the  varying 
kinds  of  resistance,  and  on  withdrawing  the  probe  carefully  will  generally 
be  able  to  determine  if  bottom  water  has  been  reached.  Should  this 
easy  method  of  examination  not  convey  all  the  needful  information,  the 
pesthole  auger  may  be  resorted  to  ;  and  it  is  desirable  that  extra  (three- 
foot)  rods  or  gaspipe  joints  be  provided  for  the  purpose  of  lengthening 
the  probe  or  auger,  when  necessary,  to  nine  or  twelve  feet.  It  will 
rarely  be  necessary  to  go  to  the  trouble  of  digging  a  pit  for  such  exam- 
inations ;  but  even  this  is  to  be  recommended  rather  than  "  buying  a 
cat  in  a  bag  "  in  the  guise  of  an  unexplored  subsoil. 

Faulty  Substrata. — A  number  of  examples  of  "  faulty 
lands,"  /.  c.,  such  as  are  underlaid  by  faulty  substrata,  are 
given  in  the  annexed  djagram  Fig.  35  ;  the  examples  being 
taken  from  California  localities  because  of  their  having  been 
most  thoroughly  investigated.  Similar  cases,  as  well  as  others 
not  here  illustrated,  of  course  occur  more  or  less  all  over  the 
world. 

Xo.  I  shows  a  case  which,  though  at  first  sight  an  aggravated 
one  of  a  rocky  substratum,  is  in  reality  that  of  some  of  the  best 
fruit  lands  in  the  State.  The  limited  surface-soil  is  very  rich, 
and  is  directly  derived  (as  a  "sedentary"  soil)  from  the 
underlying  bedrock  slate.  But  this  it  will  he  noted  stands  on 
edge,  and  the  roots  of  trees  and  vines  wedge  their  way  along 
the  cleavage  planes  of  the  slate  to  considerable  depth,  deriving 
from  them  both  nourishment  and  moisture.  Under  similar 
conditions  the  California  laurel,  usually  found  on  the  banks  of 
streams,  grows  on  the  summits  of  rocky  ridges  in  the  Coast 
Ranges. 

The  case  of  Xo.  J  is  quite  otherwise.  Here  the  shale  lies 
horizontally,  and  though  much  softer  than  the  slate  of  the  first 
column,  obstinately  resists  the  penetration  of  roots;  so  that  the 
land,  though  fairly  provided  with  plant-food,  is  almost  wholly 

12 


1/8 


SOILS. 


"    £ 

•J  .SP 


*     I. 


Ill     I     'I1  I    I1  Ml!    I,  /       ^/          "TV 

I1'  1 1  I  I  rl1!  il'   ^  r:r~s.Jlf, 

iii'ilif^ 


SOIL  AND  SUBSOIL. 


1/9 


useless  for  cultivation.  It  is  naturally  covered  with  low, 
stunted  shrubs  or  chaparral ;  only  here  and  there,  where  a  cleft 
has  been  caused  by  earthquakes  or  subsidence,  a  large  pine  tree 
indicates  that  nourishment  and  moisture  exists  within  the 
refractory  clay  stratum,  and  suggests  blasting  as  a  means  of 
rendering  the  land  fit  for  trees  at  least. 

No.  3  is  a  case  similar  to  that  of  No.  2,  only  there  is  here  a 
dense  unstratified  mass  of  red  clay,  of  good  native  fertility.  It 
is  here  that  the  expedient  of  blasting  the  tree  holes  with  dy- 
namite was  first  successfully  employed,  in  central  California. 
For  lack  of  this,  extensive  tracts  of  similar  land  in  southern 
California,  planted  to  orchards,  have  completely  failed  of  useful 
results  after  three  years  of  culture. 

No.  4  shows  a  typical  case  of  calcareous  hardpan  obstruct- 
ing the  penetration  of  roots,  even  though  usually  interrupted  at 
intervals,  because  of  the  formation  occurring  mostly  in  swales, 
along  which  the  sheets  lie  more  or  less  continuously.  Here 
also,  blasting  will  generally  permit  the  successful  growth  of 
trees  and  vines,  whose  roots  frequently  will,  in  time,  wholly 
disintegrate  the  hardpan  and  thus  render  the  land  fit  for  field 
cultures.  The  depth  at  which  such  hardpan  is  formed  usually 
depends  upon  the  depth  to  which  the  annual  rainfall  pene- 
trates. (  See  below,  page  183). 

Nos.  4,  5,  and  6  all  illustrate  cases  of  intrinsically  fertile, 
very  dee])  soils,  shallowed  by  obstructions  which  in  the  case  of 
No.  4  are  hardpan  sheets,  while  in  Xo.  5  the  intervention  of 
bottom  water  limits  root  penetration,  hence  restricts  the  use  of 
the  land  to  relatively  shallow-rooted  crops,  and  the  use  of  only 
a  few  feet  of  the  profusely  fertile  soil.  Such  is  the  case  where 
bottom  water  has  been  allowed  to  rise  too  high,  through  the 
use  of  leaky  irrigation  ditches. 

Xo.  6  illustrates  a  case  not  uncommon  in  sedimentary  lands, 
where  bottom  water  is  quite  within  reach  of  most  plants,  but  is 
prevented  from  being  utilixed  by  the  intervention  of  layers  of 
coarse  sand  or  gravel,  through  which  the  water  will  not  rise: 
rind  the  roots,  while  they  would  be  able  to  penetrate,  arc  not 
near  enough  to  feel  the  presence  of  water  underneath  and  there- 
fore spread  on  the  surface  of  the  gravel,  suffering  from  dmught 
within  easy  reach  of  abundance  of  water.  The  "  going- 
back  "  of  large  portions  of  orange  orchards  in  the  San  IVr- 


I8o 


SOILS. 


SOIL  AND  SUBSOIL.  l8l 

nardino  Valley  of  California  has  been  thus  brought  about ;  and 
unfortunately  this  state  of  things  is  almost  beyond  the  possi- 
bility of  remedy. 

Injury  from  Impervious  Substrata. — The  injurious  effects  of 
a  difficultly  penetrable  subsoil  have  already  been  discussed  and 
are  selfevident.  When  the  substratum  is  a  dense  clay,  the  rise 
of  moisture  from  below  being  very  slow,  it  can  easily  happen 
that  the  roots  cannot  penetrate  deep  enough  in  time  for  the 
coming  of  the  dry  season,  and  that  thus  the  crop  will  suffer. 
The  case  will  be  still  worse  when  hardpan  cemented  by  lime 
or  silex  limits  root-penetration,  as.  well  as  proper  drainage. 
In  such  cases  the  culture  of  field  crops  often  becomes  im- 
practicable, even  with  irrigation,  as  its  frequent  repetition,  be- 
sides being  costly,  can  rarely  be  commanded.  In  the  case  of 
trees,  the  limitation  of  root-penetration  results  in  the  spreading- 
out  of  the  roots  on  the  surface  of  the  impenetrable  layer;  as 
shown  in  figure  36,  which  exhibits  a  root-development  that 
\vould  be  quite  normal  in  the  regions  of  summer  rains,  but  is 
wholly  abnormal  in  the  arid  region,  and  results  in  the  unpro- 
fitableness or  death  of  the  trees.  It  has  often  been  attempted 
in  such  cases  to  plant  trees  in  large  holes  dug  deep  into  the  sub- 
soil and  refilled  with  surface  earth  and  manure.  All  such  at- 
tempts result  in  failure,  if  only  because  the  excavation  in- 
evitably fills  with  water,  which  will  soak  away  but  very  slowly 
into  the  dense  substrata,  and  will  thus  injure  or  drown  out  the 
roots.  Besides,  the  latter  will  remain  bunched  in  the  loose 
earth,  and  will  thus  be  unable  to  draw  either  moisture  or 
nourishment  from  the  surrounding  land.  It  is  absolutely  nec- 
essary to  remedy  this  by  loosening  the  substrata,  if  success  is 
to  be  attained. 

Shattering  of  Dense  Substrata  bv  Dynamite. — The  per- 
manent loosening  of  dense  substrata  is  best  accomplished  by 
moderate  charges  (  '  j  to  04  pounds)  of  "  Xo.  2  "  dynamite  at  a 
sufficient  depth  (3  to  5  feet).  The  shattering  effect  of  the  ex- 
plosive will  be  sensible  to  the  depth  of  eight  feet  or  more,  and 
will  fissure  the  clay  or  hardpan  to  a  corresponding  extent  side- 
wise.  If  properly  proportioned  the  charge  will  hardly  disturb 
the  surface;  but  if  this  he  desired,  from  i  '  jto  j'  j  pounds  of 
black  powder  placed  above  the  dynamite  will  throw  out  suffi- 


1 82  SOIL. 

cient  earth  to  plant  the  tree  without  farther  digging.  Where 
labor  is  high-priced  this  proves  the  cheapest  as  well  as  the  best 
way  to  prepare  such  ground  for  tree  planting ;  and  it  has  often 
been  found  that  in  the  course  of  time,  the  loosening  begun  by 
the  powder  has  extended  through  the  mass  of  the  land  so  as  to 
permit  the  roots  to  utilize  it  fully,  and  even  to  permit,  in  after 
years,  of  the  planting  of  field  crops  where  formerly  they  would 
not  succeed. 

Leachy  Substrata. — While  we  may  thus  overcome  the  dis- 
advantages of  a  dense  subsoil  or  hardpan,  there  is  another  diffi- 
culty not  uncommonly  met  with  in  alluvial  lands,  which  cannot 
be  so  readily  remedied.  It  is  the  occurrence,  at  from  two  to  six 
feet  depth,  of  coarse  sand  or  gravel,  through  which  capillary 
moisture  will  not  ascend,  but  through  which  irrigation  water 
will  waste  rapidly,  leaving  the  overlying  soil  dry.  Then 
unless  very  frequent  irrigation  can  be  given,  the  crop  will 
suffer  from  drought,  unless  indeed  the  gravel  itself  is  filled 
with  bottom  water  upon  which  the  root-ends  can  draw. 

This  case  is  a  common  one  in  the  larger  valleys  of  the  arid 
region,  and  in  time  of  unusual  drought  the  sloughs  originally 
existing,  but  since  filled  up,  will  be  clearly  outlined  by  the  dying 
crops,  while  outside  of  the  old  channels  there  may  be  no  suffer- 
ing. 

"  Going-back  "  of  Orchards.  On  such  land  as  this,  and  on 
such  as  has  a  shallow  soil  underlaid  by  an  impervious  subsoil, 
trees  will  often  grow  finely  for  three  to  five  years;  then  sud- 
denly languish,  or  turn  yellow  and  die,  as  the  demand  of  their 
larger  growth  exceeds  what  moisture  or  plant-food  the  shal- 
low soil  and  subsoil  can  supply.  Enormous  losses  have  arisen 
from  this  cause  in  many  portions  of  the  arid  region,  but  more 
especially  in  California,  owing  to  the  implicit  confidence  re- 
posed even  by  old  settlers,  and  still  more  by  newcomers,  in  the 
excellence  of  the  lands,  as  illustrated  by  farms  perhaps  a  short 
distance  away,  but  differently  situated  with  respect  to  the 
country  drainage  and  the  geological  formations.  All  such 
disappointments  could  have  been  avoided  by  an  intelligent  ob- 
servation of  the  substrata,  either  by  probing  or  digging.  Im- 
portant as  is  such  preliminary  examination  in  the  region  of 
summer  rains,  it  is  a  vitally  needful  precaution  in  the  arid 


SOIL  AND  SUBSOIL.  183 

region,  where  the  margin  between  adequate  and  inadequate 
depth  of  soil  and  moisture-supply  is  much  smaller. 

When  farmers  note  such  distress  in  the  orchard,  the  first  idea  usually 
is  that  fertilization  is  needed.  This  in  the  almost  universally  very  rich 
lands  of  the  arid  region  is  rarely  the  case  until  after  many  years  of 
exhaustive  cultivation,  and  is  scarcely  ever  of  more  than  passing  benefit 
in  such  cases.  The  first  suggestion  should  always  be  an  examination  oj 
the  substrata,  and  especially  of  the  deeper  roots ;  in  the  diseased  or 
thirsty  condition  of  which  the  cause  of  the  "die-back"  or  yellowing 
will  commonly  be  found.  Of  course  no  amount  of  fertilization  can 
permanently  remedy  such  a  state  of  things,  arising  from  impervious 
substrata,  coarse  gravel,  or  shallow  bottom  water. 

Hardpan. — By  "  hardpan  "  is  understood  a  dense  and  more 
or  less  hardened  layer  in  the  subsoil,  which  obstructs  the  pene- 
tration of  both  roots  and  water,  thus  materially  limiting  the 
range  of  the  former  both  for  plant-food  and  moisture,  and 
giving  rise  to  the  disadvantages  following  such  limitation,  as 
described  in  the  case  of  dense  subsoils.  The  hardpans  proper 
differ  from  the  latter,  however,  in  being  usually  of  limited 
thickness  only;  the  direct  consequence  of  their  mode  of  forma- 
tion, which  is  not  direct  deposition  by  water  or  other  agencies, 
but  the  infiltration  of  cementing  solutions  into  a  pre-existing 
material  originally  quite  similar  to  that  of  the  surface  soil. 
Such  solutions  usually  come  from  above,  more  rarely  from  be- 
low, and  are  of  very  various  composition.  The  solutions  of 
lime  carbonate  in  carbonated  water  have  already  been  referred 
to  in  this  connection;  as  has  also  the  fact  that  corresponding 
solutions  of  silica,  associated  more  or  less  with  other  products 
of  rock  decomposition  (  see  chapters  2  and  4)  are  constantly 
circulating  in  soils.  The  surface  soil  being  the  portion  where 
rock-weathering  and  other  soil-forming  processes  are  most 
active,  these  solutions  are  chiefly  formed  there;  and  according 
as  their  descent  into  the  substrata  is  unchecked,  or  is  liable  to 
be  arrested  at  some  particular  level,  whether  by  pre-existing 
close-grained  layers  or  by  the  cessation  of  rains,  the  subsequent 
penetration  of  air,  and  evaporation  of  the  water  alone  by  shal- 
low-rooted plants,  may  cause  the  accumulation  of  the  dissolved 
matter  at  a  certain  level,  year  after  year.  Fimllv  there  is 


1 84  SOIL- 

formed  a  subsoil-mass  more  or  less  firmly  cemented  by  the  dis- 
solved matters,  sometimes  to  the  extent  of  stony  hardness 
(lime  carbonate  in  the  arid  regions,  kankar  of  India),  more 
usually  soft  enough  to  be  penetrated  by  the  pick  or  grubbing 
hoe,  and  sometimes  by  the  stronger  roots  of  certain  plants; 
but  resisting  both  the  penetration  and  the  assimilation  of  plant 
food  by  the  more  delicate  feeding  roots. 

Nature  of  the  Cements. — The  nature  of  the  cements  that 
serve  to  consolidate  the  hardpan  mass  is  substantially  the  same 
as  those  already  mentioned  in  the  discussion  of  sandstones 
(chapt.  4,  p.  55)  ;  with  the  addition  of  those  formed,  usually 
in  connection  with  siliceous  solutions,  by  the  acids  of  the  humus 
group.  The  latter  class  of  hardpans  is  especially  conspicuous 
in  the  case  of  swampy  ground  and  damp  forests,  where  "  moor- 
bedpan  "  and  reddish  "  ortstein  "  (the  latter  particularly  devel- 
oped in  the  forests  of  northern  Europe,  where  it  has  been 
studied  in  detail  by  Miiller  and  Tuxen  1,  are  characteristic. 
The  latter  gives  for  a  characteristic  sample  of  the  reddish  hard- 
pan  underlying  a  beech  forest  in  Denmark  a  content  of  from 
2. 20  to  4.40%  of  ulmic  compounds,  and  shows  that  the  color 
is  due  to  these  and  not,  as  had  been  supposed,  to  ferric 
oxid,  which  is  present  only  in  minute  quantities. 

Bog  ore,  Moorbedpan,  Ortstein. — It  is  otherwise  with  moor- 
bedpan,  which  often  consists  of  a  mass  of  bog  iron  ore  per- 
meated or  less  with  humous  substances,  which  impart  to  it  the 
dark  brown  tint  so  often  seen  also  in  the  "  black  gravel  "  spots 
of  badly-drained  land.  On  the  whole,  however,  ferric  cements 
are  much  less  frequently  found  in  hardpans  than  in  sandstones 
formed  above  ground. 

Clay  substance  washed  from  the  surface  into  the  subsoil  by 
rains  (chapter  10,  p.  161)  always  helps  materially  to  render 
the  hardpan  impervious  when  afterwards  cemented,  a  much 
smaller  proportion  of  the  cementing  material  sufficing  in  that 
case  to  form  a  solid  layer.  In  such  cases  however  the  cement 
is  rarely  of  a  calcareous  nature,  since  lime  prevents  the  diffu- 
sion and  washing-down  of  the  clay.  It  is  mostly  siliceous  or 
zeolitic;  if  the  former,  acid  will  have  little  or  no  effect  upon 
the  solidity  of  the  hardpan ;  while  if  zeolitic,  acid  will  pretty 

1  See  ''  Studien  iiber  die  natiirlichen  Humusformen,"  by  Dr.  P.  E.  Miiller. 


SOIL  AND  SUBSOIL.  185 

promptly  disintegrate  it.  The  presence  of  humus  acids  in  the 
cements,  if  not  apparent  to  the  eye,  is  readily  demonstrated  by 
immersing  the  hardpan  fragment  in  ammonia  water  or  a  weak 
solution  of  caustic  soda ;  when  if  humus  acids  are  the  main 
cementing  substance  the  fragment  will  fall  to  crumbs,  or  be 
softened  to  an  extent  corresponding  to  the  amount  of  the 
humus  present.  Calcareous  hardpan  is,  of  course,  readily 
recognized  by  its  quick  disintegration  by  dilute  acid,  with 
evolution  of  carbonic  gas. 

In  "alkali"  soils  containing  sodic  carbonate  ("black- 
alkali  ")  there  is  commonly  found  at  the  depth  of  two  or  three 
feet  an  exceedingly  refractory  hardpan  resulting  from  the 
accumulation  of  puddled  clay  (see  above  chapt.  4,  p.  62)  in 
the  subsoil,  or  sometimes  even  on  the  surface  of  depressed 
spots.  This  hardpan,  easily  destroyed  by  the  use  of  gypsum 
and  water,  is  described  more  in  detail  in  chapter  22,  on  alkali 
soils ;  it  blues  red  litmus  paper  instantly. 

The  Causes  of  Hardpan. — The  recognition  of  the  cause  of 
hardpan  is  of  considerable  importance  to  the  farmer,  because 
of  the  influence  of  the  nature  of  the  cement  and  the  causes  of 
its  formation  upon  the  possibility  and  methods  of  its  destruc- 
tion, for  the  improvement  of  the  land. 

It  may  be  said  in  general  that  inasmuch  as  the  cause  of  the 
formation  of  hardpan  is  a  stoppage  of  the  water  in  its  down- 
ward penetration,  the  re-establishment  of  that  penetration  will 
tend  to  prevent  additional  induration;  moreover,  experience 
proves  that  whenever  this  is  accomplished  even  locally,  as 
around  a  fruit  tree  in  an  orchard,  the  hardpan  gradually 
softens  and  disappears  before  the  frequent  changes  in  moisture- 
conditions  and  the  attack  of  roots.  The  use  of  dynamite  for 
this  purpose  in  California  has  already  been  referred  to;  it  seems 
to  be  the  only  resort  when  the  hardpan  lies  at  a  considerable 
depth.  When  it  is  within  reach  of  the  plow,  it  may  be 
turned  up  on  the  surface  by  the  aid  of  a  subsoiler  and  will 
then  gradually  disintegrate  under  the  influence  of  air.  rain  and 
sun.  But  when  the  hardpan  is  of  the  nature  of  moorbedpan, 
containing  much  humic  acid  and  perhaps  underlaid  by  lx>g 
iron  ore.  the  use  of  lime  on  the  land  is  indicated,  and  will  in  the 
course  of  time  destroy  the  hardpan  layer.  This  is  the  more 
desirable  as  in  such  cases  the  surface  soil  is  usually  completely 


1 86  SOILS. 

leached  of  its  lime  content,  and  is  consequently  extremely  un- 
thrifty. 

Woodlands  of  northern  countries  bearing  beech  and  oak  are 
especially  apt  to  be  benefited  by  the  action  of  lime  on  the 
"  raw,"  acid  humous  soil  and  underlying  hardpan,  which  is 
commonly  underlaid  by  a  leaden-blue  sandy  subsoil  ("Blei- 
sand  "  of  the  Germans,  "  Podzol  "  of  the  Russians)  colored 
brown  by  earth  humates  and  mostly  too  moist  in  its  natural 
condition  to  permit  of  adequate  aeration.  These  soils  are 
usually  of  but  moderate  fertility,  and  are  best  suited  to  forest 
growth  unless  somewhat  expensive  methods  of  improvement 
can  be  put  into  practice. 

"  Plowsole." — An  artificial  hardpan  is  very  commonly 
formed  under  the  practice  of  plowing  to  the  same  depth  for 
many  consecutive  years.  The  consolidated  layer  thus  created 
by  the  action  of  the  plow  (hence  known  as  plowsole)  acts 
precisely  like  a  natural  hardpan,  and  is  sometimes  the  cause  of 
the  formation  of  a  cemented  subsoil  crust  simulating  the  nat- 
ural product.  This  is  most  apt  to  occur  in  clayey  lands,  and 
greatly  increases  the  difficulty  of  working  them,  while  detract- 
ing materially  from  the  higher  productiveness  commonly  at- 
tributed to  them  as  compared  with  sandy  lands.  Of  course  it 
is  perfectly  easy  to  prevent  this  trouble  by  plowing  to  different 
depths  in  consecutive  years,  and  running  a  subsoil  plow  from 
time  to  time.  In  this  case,  also,  lime  will  generally  be  very 
useful  and  be  found  to  aid  materially  in  the  disintegration  of 
the  "  plowsole." 

It  is  hardly  necessary  to  insist  farther  upon  the  need  of  the 
examination  of  land  to  be  occupied,  for  the  existence  of  hard- 
pan  or  other  faulty  subsoil,  which  may  totally  defeat  for  the 
time  being  the  farmer's  efforts,  or  make  him  lose  his  invest- 
ment in  plantations  after  a  few  years.  Probing  by  means  of 
the  steel  rod  described  above  (p.  177)  or  boring  with  a  post- 
hole  auger;  or  finally,  if  necessary,  digging  a  pit  to  the  proper 
depth  (from  four  to  six  feet  in  the  arid  region),  should 
precede  every  purchase  of  new  or  unexplored  agricultural 
land. 

Marly  Substrata. — Among  the  causes  of  failure  occasionally 
found  in  the  case  of  the  "  going-back  "  of  orchards,  is  the 


SOIL  AND  SUBSOIL.  187 

occurrence  of  strongly  calcareous  or  marly  substrata,  at  depths 
which  in  the  humid  region  would  not  be  reached  by  the  roots, 
but  in  the  course  of  a  few  years  are  inevitably  penetrated  by  the 
roots  of  trees  in  the  arid  region.  Then  there  appears  a  stunt- 
ing of  the  growth,  and  sometimes  a  yellowing  of  leaves,  or 
chlorosis,  due  to  the  influence  of  excessive  calcareousness  at  the 
depth  of  four  or  five  feet.  For  this  of  course  there  is  no 
remedy  except  the  planting  of  crops  which,  like  the  mulberry, 
Texas  grapes,  Chicasaw  plum  and  others,  are  at  home  on  such 
lands;  which  in  the  Eastern  states  are  naturally  occupied  by 
the  crab  apple,  honey  locust  and  wild  plums. 


CHAPTER  XI. 

THE  WATER  OF  SOILS. 

HYGROSCOPIC  AND   CAPILLARY  MOISTURE. 

WHEN  it  is  remembered  that  from  65  to  over  90%  of  the 
fresh  substance  of  plants  consists  of  water,  the  importance  of  an 
adequate  and  regular  supply  of  the  same  to  growing  plants  is 
readily  understood.  But  it  seems  desirable,  before  discussing 
the  relations  of  water  to  the  soil  and  to  plant  life,  to  consider 
first  the  physical  peculiarities  which  distinguish  it  from  nearly 
all  other  substances  known.  That  it  is  colorless,  tasteless,  in- 
odorous, and  also  chemically  neutral,  alone  constitutes  a  group 
of  properties  scarcely  found  in  any  other  fluid.  But  its  special 
adaptation  to  its  functions  in  relation  to  vegetable  and  animal 
life  are  much  more  fundamental,  as  is  shown  in  the  table  of  its 
physical  constants  as  compared  with  other  well-known  sub- 
stances, given  below. 

PHYSICAL  FACTORS   OF  WATER    COMPARED    WITH    OTHER    SUBSTANCES   (PER   UNIT 

WEIGHT). 


Capillary  ascent  in  glass  tubes 
of  one  mm.  diameter. 

^^ater  .    .    .  .                     14  mm. 

Specific  Heats. 
VVatpr  .  .            .  .  T.noo 

Heat  of  Evaporation. 

Water  at    20°  C  .613  Cal. 
"       "  100°  C.637     " 
Alcohol  ?r>o     " 

Alcohol  6  mm'.ilce  zcf 

Olive  oil  i  mm. 

HEAT  RELATIONS. 
Density. 

Water  at  o°  C.  (freezing 
pt.)...                           .   .00088 

Steam  475 
Clay,   Glass...   .i8o-.2OO 
Charcoal  241 

Spirits     of 
pentine. 

Tur- 
.  67     u 

Wood  032 

Gold,  Lead  O32-.O3I 
Zinc  00,6 

Steel  119 

Heat  of  fusion. 

Water  (Ice).  .  .     80    Cal. 
Metals  5-28       " 

Water  at  4    (Maximum 
density)  i  ooooo 

Water  at  15°  C.   (ordi- 
nary temperature).  ..   .990 
Ice  at  o°  (freezing  pt.).  .92800 

Salts,  (incl.  sili- 
cates)    40—63     " 

Summarizing  the  meaning  of  the  data  given  in  the  above 
table  with  respect  to  organic  life,  we  see,  first,  that  water  rises 
higher  both  in  the  soil  and  in  the  tissues  of  the  plant  than  any 

188 


THE  WATER  OF  SOILS.  189 

other  liquid.  Second,  that  as  its  density  decreases  in  cooling 
after  a  certain  point  is  reached,  it  freezes  at  the  surface  instead 
of  at  the  bottom,  as  other  liquids  do;  and  as  solid  water  (ice) 
is  lighter  than  fluid  water,  ice  stays  at  the  surface  and  is  readily 
melted  when  spring  comes.  Third,  since  its  temperature 
changes  more  slowly  than  that  of  any  other  liquid,  it  serves  to 
prevent  injuriously  rapid  changes  of  temperature  in  plants  and 
animals  as  well  as  in  soils.  Its  high  "  heat  of  fusion  "  also 
serves  to  prevent  quick  freezing  of  plant  and  animal  tissues,  so 
that  the  hrief  prevalence  of  a  low  temperature  may  be  more 
readily  borne.  Finally,  the  large  amount  of  heat  absorbed  in 
evaporation  of  water  serves  to  keep  both  plants  and  animals 
cool  under  excessive  external  temperatures  which  would  other- 
wise quickly  destroy  life. 

Capillarity  or  Surface  Tension. — In  this  table  it  will  be 
noted,  first,  that  water  rises  higher  in  fine  ("capillary")  or 
hair  tubes  than  the  other  fluids  mentioned,  which  fairly  rep- 
resent all  others.  Xo  other  fluid  approaches  water  in  the 
height  to  which  it  will  rise  l  in  either  soils  or  plant  tissues. 
Were  its  capillary  factor  no  higher  than,  c.  g.,  that  of  oil  or 
alcohol,  trees  could  not  grow  as  tall  as  we  find  them,  and  the 
water  supply  from  the  substrata,  and  all  the  movements  of 
water  in  the  soil,  and  hence  plant  growth,  would  be  similarly 
retarded.  It  is  easy  to  verify  these  differences  by  immersing 
a  cylinder  of  clay  soil  (or  a  cotton  wick)  in  water  on  the 
one  hand,  and  in  oil  or  alcohol  on  the  other.  Notwithstanding 
the  greater  fluidity  of  alcohol  as  compared  with  water,  the 
latter  will  be  found  to  fill  the  porous  mass  much  more 
quickly. 

The  smaller  the  diameter  of  the  tube,  the  higher  will  the  water  rise 
in  it,  and  the  greater  will  be  the  curvature  of  its  upper  surface,  to  which 
the  rise  is  sensibly  proportional.  Hut  in  the  case  of  liquids  which  do 
not  "  wet  "  the  walls  of  the  tube  (as  in  that  of  mercury  and  glass),  the 
curve  (meniscus)  is  convex,  instead  of  concave,  and  the  liquid  is 
depressed  instead  of  rising. 

It  is  in  its  relations  to  heat,  however,  that  water  is  specially 
distinguished  from  other  substances;  and  these  differences  are 

1  Excepting  only  the  water-solutions  of  certain  salts,  among  which  common 
salt,  kainit  and  nitrate  of  soda  are  of  agricultural  interest.  Common  salt  may  in- 
crease the  capillary  rise  to  the  extent  of  more  than  live  percent. 


190  SOILS. 

most  vital  not  only  to  living  organisms,  but  to  the  entire  econ^ 
omy  of  Nature. 

Density. — As  regards  the  density  or  specific  gravity  of  water 
(which  is  by  common  consent  assumed  as  the  unit  of  com- 
parison), it  will  be  seen  from  the  "  Density  "  table  that  whereas 
all  other  bodies  contract  and  become  more  dense  as  they  grow 
colder,  water  has  its  point  of  (fluid)  "  maximum  density  "  at 
4°  C.  (49°. 2  Fahr),  and  expands  as  it  grows  colder,  until  at 
o°  C.  (32°  Fahr.)  it  solidifies  into  ice.  In  so  doing  it  de- 
parts still  farther  from  the  rule  obtaining  \vith  all  other  bodies 
(excepting  certain  mixtures,  such  as  type  metal)  and  again  ex- 
pands so  as  to  decrease  the  density  from  .99988  to  .92800 ;  thus 
causing  ice  to  float  on  water  at  the  freezing  point.  Hence 
water,  unlike  all  other  fluids,  solidifies  first  on  the  surface ;  and 
but  for  this,  the  thawing  of  the  winter's  ice,  which  would  be 
formed  at  the  bottom  of  rivers  and  lakes,  would  be  deferred 
until  late  in  summer.  The  expansion  of  water  in  freezing  is 
forcibly  illustrated  in  the  bursting  of  water  pipes  and  pitchers 
in  winter;  in  the  soil,  the  ice  forming  in  the  interstices  serves 
to  loosen  the  compacted  land  and  give  it  better  tilth  for  the  en- 
suing season. 

Specific  Heat. — Considering  next,  the  column  showing  the 
"  specific  heat  "  of  water  as  compared  with  other  substances,  we 
see  that  it  exceeds  all  other  known  bodies  in  the  amount  of  heat 
required  to  change  its  temperature;  hence  again,  its  heat  capa- 
city is  taken  as  the  unit  to  which  all  others  are  compared.  The 
figures  given  in  the  table  show  that  even  ice  and  steam  require 
for  equal  weights  only  about  half  as  much  heat  (or  burning  of 
fuel)  to  change  their  temperature  (c.  g.,  i  degree)  as  would 
liquid  water.  But  earthy  matters,  such  as  clay  or  soil  and 
glass,  require  only  one-fifth  as  much  heat  for  a  similar  change; 
charcoal  only  about  one-fourth  as  much.  But  vegetable  mat- 
ter as  represented  by  wood  on  the  one  hand,  and  gold  and  lead 
on  the  other,  require  only  about  one-thirtieth  as  much  heat  as 
an  equal  weight  of  water;  zinc  about  one-tenth  as  much,  steel 
somewhat  more. 

It  is  thus  plain  that  masses  of  water  act  powerfully,  more 
than  any  other  substance,  as  moderators  of  changes  of  temper- 
ature by  their  mere  presence.  The  body  of  an  animal  or 
plant  is  protected  against  violent  changes  by  the  presence  of 


THE  WATER  OF  SOILS.  I9I 

from  60%  to  90%  of  liquid  water,  the  temperature  of  which 
can  only  be  raised  or  lowered  slowly ;  a.nd  the  presence  of  the 
sea  tempers  the  climates  of  coasts  and  islands  as  compared  with 
the  heat  or  cold  occurring  in  the  interior  of  the  continents. 

Ice. — Again,  it  is  shown  in  the  table  that  the  heat  required 
to  melt  ice  is  greater  than  in  the  case  of  any  other  substance, 
especially  the  metals;  which  when  once  heated  to  the  fusing 
point,  require  only  a  very  little  more  heat  to  become  liquid. 
The  fusion  of  salts  (including  silicate  rocks)  requires  more 
heat  than  does  that  of  the  pure  metals. 

Valorization. — In  the  amount  of  heat  required  for  its  vapor- 
ization water  is  also  especially  pre-erninent,  and  potent  in  its 
influence  upon  organic  life.  The  table  shows  that  the  evapor- 
ation of  water  requires  six  hundred  heat  units  l  as  compared 
with  alcohol,  requiring  only  two  hundred ;  while  spirits  of 
turpentine,  the  representative  of  a  large  proportion  of  vegetable 
fluids,  needs  but  sixty-seven. 

The  practical  result  is  that  evaporation  of  water  from  the 
surface  of  animals  and  the  leaves  of  plants,  is  exceedingly 
effective  in  preventing  excessive  rise  of  temperature,  the  heat 
of  the  sun  and  air  being  spent  in  evaporating  the  perspiration 
of  animals  and  plants  before  an  injurious  rise  of  temperature, 
such  as  would  cause  sunstroke  in  animals,  and  wilting  or  with- 
ering in  plants,  can  occur.  But  since  evaporation  is  most  rapid 
in  dry  air,  it  follows  that  the  cooling  effect  will  be  the  greater 
in  the  arid  regions  than  in  the  humid.  In  the  latter,  therefore, 
sunstroke  is  much  more  frequent  than  in  the  fervid  regions  of 
the  arid  west,  even  though  the  temperature  in  the  latter  may  be 
higher  by  twenty  or  twenty-five  degrees  Fahrenheit.  White 
men  who  would  soon  succumb  if  they  attempted  to  work  in  the 
sun  in  Mississippi  or  Louisiana  when  the  thermometer  stands 
at  95 °F.  will  experience  no  inconvenience  under  the  same  con- 
ditions in  the  dry  atmosphere  of  the  (ireat  Valley  of  California. 

Solvent  /'o^rr. — To  the  exceptional  properties  of  water  dis- 
cussed above,  should  be  added  another  hardly  less  important 
one.  viz..  that  of  being  an  almost  universal  solvent  especially  of 

'  A  heat  unit,  or  "  calorie,"  is  the  amount  of  heat  required  to  raise  the  tempera- 
ture of  a  unit-weight  (pound,  kilogram,  or  gram)  of  water  one  thermometric  degree. 
According  to  the  unit-weight  and  thermometric  scale  used,  the  figures  will  vary, 
but  in  this  text  the  basis  is  understood  to  be  kilograms  and  the  centigrade  scale. 


192 


SOILS. 


mineral  matters,  including  even  those  which,  like  quartz,  appear 
to  be  most  insoluble  and  refractory  (see  chapt.  3).  The  water 
of  the  soil  is  thus  enabled  to  convey  to  the  roots  of  plants,  in 
solution,  all  kinds  of  plant  food  contained  in  the  soil.  It 
should  be  noted  that  distilled  (hence  also  rain-)  water  is  a 
more  powerful  solvent,  e.  g.,  of  glass,  than  ordinary  waters 
containing  mineral  matter,  and  even  free  acids. 

Practically,  plants  take  up  all  their  water  supply  f rom/the  soil 
in  the  liquid  form ;  and  hence  the  soil-conditions  with  respect  to 
this  supply  are  of  the  most  vital  importance  to  plant  growth. 
The  most  abundant  supply  of  mineral  plant  food  may  be  wholly 
useless,  unless  the  physical  conditions  of  adequate  soil-mois- 
ture, access  of  air,  and  warmth,  are  fulfilled  at  the  same  time. 
On  the  other  hand,  comparatively  few  plants  are  adapted  to 
healthy  growth  in  soils  saturated  with  water,  or  in  water 
itself;  and  but  few  among  these  are  of  special  interest  from 
the  agricultural  standpoint. 

Water-requirements  of  Growing  Plants. — The  amount  of 
water  contained  in  any  plant  at  one  time,  however  large,  is  but 
a  small  proportion  of  what  is  necessary  to  carry  it  through  its 
full  development.  When  we  measure  the  amount  of  water 
actually  evaporated  through  the  plant  in  the  course  of  its  nor- 
mal growth,  we  find  it  to  be  several  hundred  times  the  quantity 
of  dry  vegetable  substance  produced ;  varying  according  to  the 
extent  and  structure  of  the  leaf-surface,  the  number  and  size 
of  the  breathing  pores  (stomata)  of  the  leaves,  and  the 
climatic  conditions  (including  specially  the  duration  of  active 
vegetation,  and  temperature  during  the  same),  from  225  to 
as  much  as  912  times  the  weight  of  the  mature,  dry  plant. 

The  following  are  extreme  figures  for  water  consumption  of 
different  plants  as  reported  by  different  observers,  viz.,  Lawes 
and  Gilbert  in  England,  Hellriegel  in  northern  Germany, 
Wollny  in  Southern  Germany  (Munich),  and  King  in  Wis- 
consin: \Vheat,  225  to  359;  barley,  262  to  774;  oats,  402  to 
665;  red  clover,  249  to  453;  peas,  235  to  447;  mustard  and 
rape,  845  to  912  respectively;  the  latter  figure  being  the 
maximum  thus  far  reported.  The  highest  figures  given  are 
throughout  very  nearly  those  of  Wollny,  working  in  the  very 
rainy  climate  of  Munich. 

Evaporation  from  Plants  in  Different  Climates. — It  might 


THE  WATER  OF  SOILS. 


193 


be  expected  that  in  countries  where  the  air  is  usually  moist,  the 
evaporation  will,  other  things  being  equal,  be  less  than  where  it 
is  commonly  far  below  the  point  of  saturation.  But  the 
"  guardian  cells  "  (stomata)  of  the  leaf  pores  possess  the  power 
of  regulating,  to  a  certain  extent,  the  evaporation  from  the 
leaf-surface  in  accordance  with  temporarily  prevailing  condi- 
tions, so  as  to  allow  free  evaporation  in  moist  air,  but  to  pre- 
vent the  wilting  and  drying-up  of  the  leaf  in  hot  and  dry  air, 
save  in  extreme  cases.  Moreover,  plants  adapted  to  arid  condi- 
tions are  usually  provided  with  additional  safeguards  in  the 
form  of  thick,  non-conducting  layers  of  surface  cells,  or  long 
channels  connecting  the  interior  tissue  with  the  breathing- 
pores  on  the  surface.  Often  hairy,  scaly  or  viscous  coverings 
serve  the  same  end.  On  the  other  hand,  when  the  air  is  very 
moist,  so  as  to  check  evaporation,  water  is  sometimes  found 
secreted  in  minute  droplets  around  the  breathing-pores  of  the 
leaves,  since  its  ascent  is  a  necessary  condition  of  nutrition 
and  development. 

Relation  between  Evaporation  and  Plant-growth. — There  is 
not  in  all  cases  any  direct  relation  between  the  amount  of  evap- 
oration and  plant  growth;  but  experience,  as  well  as  numerous 
rigorous  experiments  have  shown  that  under  ordinary  condi- 
tions of  culture,  and  within  limits  varying  for  different  soils 
and  crops,  production  is  almost  directlv  proportional  to  the 
water  snpplv  during  the  period  of  active  vegetation. 

On  the  basis  of  Hellriegel's  results,  showing  that  wheat  uses 
(in  Germany)  about  435  tons,  or  nearly  four  acre-inches  of 
water  in  the  production  of  one  ton  of  dry  matter,  and  assuming 
the  ratio  of  grain  to  straw  to  be  i  :i.5.  King  calculates  the 
following  table  of  probable  production  under  different  moisture 
conditions  (  Physics  of  .Agriculture,  page  140)  : 


YIKI.I)    I'KK    ACKK. 


Number  of 

Weight  of  (Jraiu. 

Weight  of  Straw. 

Total  Weight. 

Water  UM-C!. 

Bushels. 

Tons. 

Tons. 

Tons. 

Acre-inches. 

15 

•45 

675 

1.125 

4--40S 

20 

.60 

90 

I.  sOO 

VO'.S 

?S 

•75 

I  125 

I.87S 

7-l'>7 

3° 

.00 

1  .15° 

2.2^O 

S  .1-17 

35 

1.05 

1  575 

2.fi25 

10.495 

40 

1.20 

i  Soo 

3-OOO 

i  r.ooo 

194 


SOILS. 


S.  Fortier  has  made  several  series  of  tests  to  determine  the 
actual  yield  of  grain  crops  under  field  conditions  when  sup- 
plied with  different  amounts  of  water.  Two  of  these  were 
made  at  the  Montana  experiment  station  in  1902  and  1903, 
(see  reports  of  these  years),  in  large  tanks  placed  in  a  field, 
level  with  the  ground.  The  results  of  the  last  year's  experi- 
ments are  shown  graphically  in  the  figure  below,  from  which 

it  will  be  seen  that  the 
yield  increased  quite  regu- 
larly with  the  amount  of 
water  supplied,  up  to  the 
depth  of  36  inches  of 
water. 

It  should  be  noted  that 
in  this  case  (and  as  usual) 
not  only  the  quantity  but 
the  quality  of  the  grain 
was  greatly  improved  as 
the  water-supply  in- 
creased, it  becoming 
larger  and  more  uniform 
in  size. 

Of  similar  experiments 
made  in  the  San  Joaquin 
Valley,  California,  in 
1904,  Fortier  says:1 

"In  e  x  p  e  r  i  m  enting 
with  barley  last  winter 

FIG.   37. — Experiments  on  Cereal   production   with       ,  '.  _.,..- 

various    amounts  of   water   (Fortier,    Report     Mont.     1  rainiail, 

ExPt.  sta.,  1903).  which    amounted    to    4^2 

inches  during  the  period  of  growth,  produced  at  the  rate  of 
nine  bushels  per  acre,  while  the  application  of  sixteen  inches 
of  water  increased  the  yield  to  twenty-two  bushels  per  acre. 
In  the  same  case;  of  wheat,  the  rainfall,  alone,  produced  straw, 
but  no  grain ;  four  inches  of  additional  irrigation  water  pro- 
duced a  yield  at  the  rate  of  ten  bushels,  and  sixteen  inches  of 
water  increased  the  yield  to  thirty-eight  bushels  per  acre." 


"  Water  and  Forest,"  January,  1905.     "  The  Use  of  Water,"  by  S.  Fortier. 


THE  WATER  OF  SOILS.  195 

It  is  thus  obvious  that,  other  things  being  equal  and  with 
conditions  sufficiently  favorable  for  the  growth  of  crops,  the 
rule  as  formulated  above  is  verified  in  practice. 

Whitney  (Bulletin  22,  Bureau  of  Soils,  U.S.  Dept.  Agr.),  has  carried 
this  rule  so  far  as  to  claim  that  in  all  soils,  the  moisture  supply  is  the 
only  important  factor,  and  that  so  long  as  this  is  provided  for,  soil 
fertility  continues  indefinitely  without  replacement  of  ingredients  with- 
drawn. The  latter  conclusion  is  so  thoroughly  disproved  by  experience 
as  well  as  experiment  that  it  hardly  requires  discussion  here. 

Whether  plants,  especially  cultivated  ones,  are  capable  of 
adapting  themselves  to  arid  conditions  so  as  to  be  capable  of 
producing  satisfactory  crops  with  less  water  than  is  actually 
consumed  in  the  humid  region,  has  not  been  directly  deter- 
mined. Such  is,  however,  the  impression  produced  by  farming 
experience;  and  the  fact  that  among  the  common  weeds  of  arid 
California  are  mustard  and  rape,  cited  by  Wollny  as  requiring 
over  three  times  as  much  water  as  does  maize  for  the  pro- 
duction of  one  part  of  dry  matter,  lends  color  to  the  supposition 
that  in  some  manner  these,  and  probably  other  plants,  use  more 
water  in  humid  than  in  dry  climates  (see  this  chapt.  p.  212). 

It  is  therefore  impossible  to  assign  a  definite  figure  for  the 
amount  of  water  required  by  vegetation  at  large;  and  even  for 
one  and  the  same  plant,  only  approximations  conditioned  upon 
climatic  factors  can  be  given.  We  can  in  many  cases,  how- 
ever, assign  for  one  plant,  or  for  certain  groups  of  plants,  the 
amounts  of  water  producing  the  best  results  ("optimum") 
and  the  least  amount  ("  minimum  ")  compatible  with  a  paying1 
crop,  that  must  be  furnished  during  the  growing  season,  to 
produce  certain  results.  For  when  instead  of  fruiting,  it  is 
desired  that  the  crop  should  produce  the  largest  possible 
amount  of  vegetable  substance,  as  in  the  case  of  forage  crops,  a 
larger  amount  of  water  will  usually  be  serviceable. 

Different  conditions  of  Soil-li'ater. — Water  may  be  con- 
tained in  the  soil  in  three  different  conditions,  viz.  : 

1.  From  absorption  of  water  vapor;  Hygroscopic  water. 

2.  Liquid  water  held  suspended  between  the  soil  particles 
so  as  to  exert  no  hydrostatic  pressure;  capillary  water,  or  water 
of  imbibition. 

1  See  Wollny's  experiments,  Forsch.  Agr.  I'hys.  Vol.  20,  p.  58. 


196 


SOILS. 


3.  Liquid  water  seeking  its  level ;  bottom,  ground  or  hydro- 
static water. 

HYGROSCOPIC  WATER. 

Soils  artificially  dried  so  as  to  deprive  them  of  all  their  mois- 
ture, when  exposed  to  moist  air  absorb  water  vapor  with  great 
energy  at  first ;  both  the  rapidity  of  absorption  and  the  amounts 
absorbed,  when  full  time  is  given,  varying  greatly  with  their 
nature.  Sandy  soils,  broadly  speaking,  absorb  the  smallest 
amounts ;  while  clayey  soils,  and  those  containing  much  humus, 
or  finely  divided  ferric  hydrate,  take  up  the  largest  proportion. 

The  figure  expressing  the  amount  of  aqueous  vapor  absorbed 
at  the  standard  temperature  of  15°  Cent.,  is  called  the  coef- 
ficient of  moisture  absorption.  For  one  and  the  same  sub- 
stance, this  coefficient  rises  as  the  grain  becomes  finer,  the 
surface  being  correspondingly  increased  (see  chapt.  6). 

The  table  below  indicates  the  effect  of  the  three  substances 
mentioned  in  increasing  moisture  absorption  as  compared  with 
a  very  sandy  soil  from  the  pine  woods  of  Mississippi,  and  a 
gray  silt  or  "  dust  "  soil  from  Washington,  very  fine-grained 
but  poor  both  in  humus  and  ferric  hydrate.  (For  details  of 
the  physical  composition  of  the  Mississippi  soils  see  table  in 
chapt.  6,  p.  93).  A  highly  ferruginous  soil  from  Oahu  shows 
plainly  the  effect  of  that  substance. 

TABLE  SHOWING  INFLUENCE  OF   SILT,   SAND,  CLAY,   FERRIC  HYDRATE,  AND 
HUMUS  ON   MOISTURE  ABSORPTION. 


248 

79 

238 

230 

246 

22O 

215 

J2 

en 

* 

M 

<U      . 

•a 

o 

^'"s 

bp  _u 

^ 

j. 

2  rt 

3 

^-    S^ 

o  — 

3  C/) 

c  '•"* 

« 

C/3 

O 

G    . 

la  _rt 

'f.  'O 

u 

;-     >> 

tu  2 

rt  _^ 

f5 

s 

c  "5 

1^  ^ 

15 

t£  •— 

pH      ^ 

S  'J 

^  "n* 

CM      ^^ 

^  r/^ 

•    D 

'T"   ^ 

^) 

>~< 

•  1.  I 

•  'X 

•   C 

c§ 

22  -S* 

•  ~ 

t/i    a) 

3'  « 

2  ^ 

en 

in  ,y$ 

^» 

s  ^ 

<n 

S   O 

rt  O 

2 

2 

§ 

^ 

jg 

o.s 

% 

* 

% 

^ 

^ 

* 

rf 

* 

IJygr.  Moisture  

•>    48 

0.09 

977 

18.60 

in.  66  °T    <^" 

I  5.40 

Clay  

-  •  1  J 
2  *  94 

I     27 

7/1  6c 

J.) 

'"Sic 

Tr. 

Tr. 

Ferric  Hydrate  

I  .64 

1  •  "-/ 

/  *T  '  ^J 

•  '  S 

-5-4 

_U.    1   ^ 

12.  IO 

41  .00 

Humus         

'  '44. 

o.oo 

'  '  io 

little 

7    77  f*Ti    in 

19.83 

Finest  Silts  (OI-.O25O  mm.).  .  . 
Sands,  f.  and  c.  (-O25O-.5O  mm.) 

60.  io 

31.20 

45.04 
42.40 

23.15 
.  20 

68.60 
4  7° 

40.33 
15.61 

J'  Jj 
[45.66 

33-94 

8.70 
70.18 

THE  WATER  OF  SOILS.  197 

It  will  be  noted  that  the  greater  fineness  of  grain  in  the 
Washington  dust  soil  induces  a  higher  absorption  of  moisture 
than  occurs  in  the  sandy  soil  from  Mississippi,  although  the 
latter  contains  more  clay.  Comparison  of  the  figure  for  the 
Mississippi  pipeclay  and  clay  soil  with  the  ferruginous  soils, 
from  the  same  state  and  from  Oahu,  indicate  plainly  the  in- 
fluence of  the  ferric  hydrate  in  increasing  absorption ;  although 
in  the  latter  case  the  clay  determination  was  not  made,  because 
of  the  excess  of  ferric  hydrate.  The  influence  of  humus  is 
plainly  shown  in  the  case  of  the  marsh  muck  and  soil,  neither 
of  which  contain  any  appreciable  amount  of  either  clay,  or  fer- 
ric hydrate  in  the  finely  diffused  condition.  The  relatively 
slight  difference  in  the  absorptions  of  muck  and  soil  is  due  to 
the  only  partial  humification  of  the  organic  matter  in  the 
former,  while  in  the  soil  the  humification  is  sensibly  complete, 
and  the  sand  forming  the  body  of  the  material  serves  to  render 
it  more  loose. 

These  data,  referring  to  natural  materials,  while  not  as  com- 
plete as  could  be  desired,  are  sufficient  to  prove  the  facts,  and 
seem  preferable  to  any  artificially  devised  imitation  of  their 
kind. 

Influence  of  Temperature,  and  Degree  of  Air-Saturation. — 
The  amount  of  moisture  absorbed  varies  materially  both  with 
the  temperature,  and  with  the  degree  of  saturation  of  the  air 
to  which  the  soil  is  exposed.  Schiibler,  Knop  and  other  earlier 
observers,  operating  with  earth  exposed  to  air  only  partly 
saturated,  and  with  soil  layers  of  considerable  thickness  (in 
watch  glasses),  found  that  the  absorption  decreased  as  the 
temperature  increased,  according  to  a  law  formulated  by  Knop. 
The  writer  found  that  under  the  conditions  established  in  the 
experiments  of  Knop  and  others,  the  air  was  not  nearly  satur- 
ated,1 so  that  these  determinations  are  marred  by  ineliminable 

1  It  should  he  understood  that  it  is  by  no  means  easy  to  insure  full  saturation 
in  any  considerable  volume  of  air. 

It  has  generally  been  considered  sufficient  to  cover  with  water  the  bottom  of 
the  space  in  which  absorption  was  to  occur.  The  writer  found  that  in  order  to 
insure  uniform  results,  it  was  necessary  to  cover  the  entire  inner  surface  of  the 
vessel  with  wet  blotting  paper,  and  even  then  to  exclude  carefully  all  circulation 
of  air  by  padding  the  joints  with  such  paper.  When  only  the  bottom  of  the  box 
was  covered,  samples  placed  at  different  levels  above  the  water  surface  gave  dis- 
cordant results.  It  was  also  observed  that  whenever  the  thickness  of  the  soil 


198  SOILS. 

faults,  the  more  as  the  soils  used  are  only  designated  in  general 
terms,  as  "  garden  soil,"  "  loam,"  "  peaty  land,"  etc.,  without 
any  definite  indication  of  their  actual  physical  or  chemical  con- 
stitution. The  writer  therefore  undertook  to  correlate  these 
coefficients,  determined  with  respect  to  completely  saturated 
air,  with  the  physical  composition  of  certain  soils,  as  deter- 
mined by  means  of  the  methods  heretofore  described. 

Some  of  the  data  so  obtained  are  given  in  the  table  of  physical  soil 
composition  on  page  93,  chapt.  6.  They  have  since  been  extensively 
supplemented  by  additional  determinations,  but  without  materially 
changing  the  coefficients  approximately  corresponding  to  the  several 
designations  accepted  in  farm  practice.  Experiments  conducted  by 
the  writer  have  conclusively  shown  that  Knop's  law  of  decrease  of 
absorption  with  rise  of  temperature  not  only  is  not  true  for  fully  saturated 
air,  but  must  be  reversed ;  the  fact  being  that  the  amount  of  water 
absorbed  by  the  soil  increases  in  a  fully  saturated  atmosphere  (i.e.,  in 
presence  of  excess  of  water)  as  the  temperature  rises,  at  least  between 
15  and  35  degrees  Cent.  Thus,  fine  sandy  soil  which  at  15°  absorbed 
2°/0  of  moisture,  took  up  4%  at  34°  ;  while  loam  soil  absorbing  7  %  at 
15°,  showed  nearly  9%  at  35°  ;  an  increase  of  2%  in  each  case.  But 
in  partially  saturated  air  a  it  was  found  that,  as  stated  by  Knop,  the 
amounts  absorbed  steadily  decrease,  though  not  according  to  the  law 
announced  by  him.  Taking  as  a  unit  the  moisture  absorbed  at  15°, 
it  was  found  that  in  air  three-fourths  saturated,  f  of  the  unit  was  taken 
up  by  the  soil ;  at  half  saturation,  nearly  the  proportional  amount ;  but 
at  one-fourth  saturation  the  earths  absorb  materially  more  than  a  similar 
proportion,  being  then  capable  of  withdrawing  moisture  from  greatly 

layer  exceeded  about  one  millimeter,  a  long  time  was  required  for  full  saturation  ; 
during  which  inevitable  changes  of  temperature  would  bring  about  a  deposition  of 
dew  on  the  soil,  greatly  exaggerating  the  absorptive  coefficient. 

In  the  chamber  used  at  the  California  station  for  soil  saturation,  dimensions  12 
X  18  X  19  inches  high,  the  same  soil  was  exposed  on  a  shelf  close  to  the  sur- 
face of  the  water,  another  midway  up,  a  third  near  the  lower  surface  of  the  cover; 
liquid  water  being  in  the  bottom  of  the  chamber,  and  the  rest  covered  with  wet 
blotters.  It  was  found  that  despite  these  precautions,  the  lowest  soil  layer 
absorbed  in  the  same  time  as  much  as  ^°/0  more  than  the  uppermost  one. 

2  The  partial  saturation  to  a  definite  extent  was  effected  by  means  of  solutions 
of  calcium  chlorid  of  different  degrees  of  concentration,  according  to  the  de- 
terminations of  Wiillner  (Pogg.  Ann.).  These  solutions  were  placed  in  a  wide, 
flat  dish,  over  which  a  layer  of  soil  i  mm.  in  thickness  was  exposed,  all  being 
covered  with  a  bell  glass  lined  inside  with  the  same  solution,  so  as  to  insure  equal 
saturation. 


THE  WATER  OF  SOILS.  199 

undersaturated  air.  Since  air  thus  undersaturated  occurs  not  uncom- 
monly in  the  arid  regions  of  the  world,  the  fact  that  the  soil  cannot  be 
farther  dried  by  such  air  of  the  same  temperature,  is  of  some  practical 
significance. 

In  view  of  the  highly  variable  composition  of  soils  and  of 
the  doubtless  varying  hygroscopic  properties  of  their  several 
physical  constituents,  it  is  not  to  be  expected  that  any  one  nu- 
merical law  will  hold  good  exactly  for  all  kinds  of  lands. 
Mineral  powders,  colloidal  clay,  ferric  hydrate,  aluminic  hy- 
drate, the  zeolites,  humus,  and  other  hydrates  known  to  occur, 
doubtless  each  follow  a  different  law  in  the  absorption  of  mois- 
ture and  gases ;  so  as  to  modify  the  hygroscopic  properties  of 
the  soil  in  accordance  with  their  relative  predominance  in  each 
case.  (See  table  of  absorption  of  gases,  chapter  14). 

Utility  of  Hygroscopic  Moisture  to  Plant-growth. — The 
early  experimenters  considered  the  hygroscopic  moisture  of 
the  soil  to  be  of  very  great  importance  to  the  welfare  of  crops. 
Within  the  last  twenty-five  years  much  doubt  has  been  cast 
upon  this  claim,  even  to  the  extent  of  stating  that  "  the 
hygroscopic  efficacy  of  soils  must  be  definitely  eliminated  from 
among  the  useful  properties  "  (Mayer's  Agriculturchemie,  vol. 
2,  p.  131).  Yet  Mayer  himself  concedes  the  cogency  of  the 
experiments  made  by  Sachs,  which  proved  that  dry  soil  im- 

1 E.  A.  Mitscherlich  (Hodenkunde  fiir  Land-und  Forstwirthe,  p.  156  et  al.) 
claims  that  all  determinations  of  soil  hygroscopicity  thus  far  made  are  grossly 
incorrect  on  account  of  the  dew  liable  to  be  condensed  on  the  soil  layer  from 
fully  saturated  air,  as  the  result  of  slight  changes  of  temperature.  lie  therefore 
would  have  all  such  determination  made  either  in  an  air-vacuum,  or  over  a  io°'0 
solution  of  sulfuric  acid. 

Such  dew-formation,  however,  cannot  happen  to  any  appreciable  extent  under 
the  conditions  maintained  in  the  writer's  work,  viz,  absorption  within  a  thick- 
walled  (two-inch)  wooden  box  of  the  dimensions  given  above,  and  sunk  in  the 
ground  in  a  cellar  in  which  the  temperature  varies  only  a  few  tenths  of  a  degree 
during  24  hours.  The  soil  layer  of  one  millimeter  thickness  being  put  down  in 
the  morning,  the  7  hour  absorption  period  falls  at  the  time  of  slightly  rising  tem- 
perature, as  an  additional  precaution  against  dew-deposition.  Mitscherlich  fails, 
moreover,  to  show  that  this  source  of  error  produces  any  wide  or  serious  dis- 
crepancies except  under  such  long  absorption  periods  as  he  finds  it  necessary  to 
use  because  of  the  great  thickness  of  his  soil  layers.  It  is  doubtful  whether  the 
limits  of  errors  in  soil  sampling  do  not  greatly  exceed  any  of  those  involved  in 
the  writer's  method,  and  whether  such  accuracy  as  is  attempted  by  Mitscherlich  is 
of  any  practical  significance. 


200  SOILS. 

mersed  in  a  (probably  not  even  fully)  saturated  atmosphere 
is  capable  of  supplying  the  requirements  of  normal  vegetation ; 
thus  explaining  the  obvious  beneficial  effects  on  vegetation  of 
the  summer  fogs  prevailing  in  portions  of  the  arid  region, 
e.  g.,  on  the  coasts  of  California  and  Chile. 

Mayer's  experiments  relied  upon  to  prove  the  uselessness  of  hygro- 
scopic moisture  to  plant  growth,  were  carried  out  in  flower-pots,  in 
which  it  was  plainly  shown  that  the  plants  wilted  before  even  the 
visible  liquid  (capillary)  moisture  of  the  earth  was  entirely  exhausted. 
But  this  simply  proves  that  under  such  artificial  conditions,  plants  can- 
not withdraw  moisture  from  the  soil  rapidly  enough  for  their  needs. 
In  nature,  and  notably  in  the  arid  regions,  the  chief  supply  of  water  is 
received  through  the  deep-going  main  roots,  while  the  bulk  of  the 
active  feeding  roots  of  the  plant  may  be  surrounded  by  almost  air-dry 
soil;  under  which  conditions,  as  Henrici  (Henneberg's  Journ.,  1863,  p. 
280)  has  shown,  slow  growth  and  nutrition  occurs  even  in  such  plants 
as  the  raspberry,  a  native  of  humid  climates.  But  in  the  arid  region 
this  is  the  normal  condition  of  the  native  vegetation  through  most  of 
the  rainless  summer.  That  a  higher  moisture-coefficient  does  not 
necessarily  imply  that  a  larger  amount  of  moisture  can  be  withdrawn 
from  the  soil  by  the  plants,  is  undoubtedly  true  in  some,  but  not  in  all 
cases ;  for  in  soils  rich  in  humus,  the  moisture  is  more  freely  shared 
with  the  roots  than  in  non-humous,  clay  lands. 

The  higher  moisture-absorption  is  however  of  the  most  un- 
questionable service  in  the  case  of  the  occurrence  of  the  hot, 
dry  winds  that  so  frequently  threaten  the  entire  crops  of  some 
regions.  In  this  case  the  soil  containing  the  greater  amount 
of  moisture  requires  a  much  longer  time  to  be  dried,  and  heated 
up  to  the  point  of  injury  to  the  roots,  than  in  the  case  of  sandy 
soils  of  low  absorptive  power,  whose  store  is  exhausted  in  a 
few  hours  and  then  permits  the  surface  to  be  heated  up  to  the 
scalding  point,  searing  the  stems  and  root  crowns.  That  such 
injury  occurs  much  sooner  in  sandy  lands  than  in  well-culti- 
vated clay  soils,  is  a  matter  of  common  note  in  the  arid  region. 

Summary. — The  significance  of  hygroscopic  moisture  in 
connection  with  plant  growth  may  then  be  thus  summarized : 

i.  Soils  of  high  hygroscopic  power  can  withdraw  from 
moist  air  enough  moisture  to  be  of  material  help  in  sustaining 


THE  WATER  OF  SOILS.  2OI 

the  life  of  vegetation  in  rainless  summers,  or  in  time  of 
drought.  It  cannot,  however,  maintain  normal  growth,  save 
in  the  case  of  some  desert  plants. 

2.  High  moisture-absorption  prevents  the  rapid  and  undue 
heating  of  the  surface  soil  to  the  danger  point,  and  thus  often 
saves  crops  that  are  lost  in  soils  of  low  hygroscopic  power. 

CAPILLARY  WATER. 

The  liquid  water  held  in  the  pores  of  the  soil,  in  the 
form  of  surface  films  representing  the  curved  surface  seen 
in  capillary  tubes,  and  therefore  tending  to  cause  the 
water  to  move  upwards,  as  well  as  in  all  other  directions, 
until  uniformity  of  tension  is  established,  is  of  vastly  higher  im- 
portance to  plant  growth  than  hygroscopic  moisture.  It  not 
only  serves  normally  as  the  vehicle  of  all  plant  food  absorbed 
during  the  growth  of  the  usual  crops,  but  also,  as  a  rule,  to  sus- 
tain the  enormous  evaporation  by  which  the  plant  maintains 
during  the  heat  of  the  day,  a  temperature  sufficiently  low  to 
permit  of  the  proper  operation  of  the  processes  of  assimilation 
and  building  of  cell  tissue. 

Comparatively  few  plants  have  roots  adapted  to  healthy  ac- 
tion while  submerged  in  water,  excluding  them  from  free  ac- 
cess of  the  oxygen  of  the  air;  and  when  such  roots  are  formed 
by  plants  not  naturally  growing  in  water  or  swampy  ground, 
they  differ  so  far  from  earth  roots  in  their  structure  that  when 
transferred  to  soil  they  usually  die,  normal  earth-roots  being 
gradually  formed  instead.  Conversely,  there  is  for  all  land 
plants  a  definite  time-limit  beyond  which  their  roots  cannot 
live,  or  at  least  remain  healthy,  in  submersion.  Thus  grain 
fields  will  with  difficulty  recover  from  a  week's  total  submer- 
sion; while  young  rice  fields  will  resist  considerably  longer. 
When  in  the  resting  (winter)  condition  vineyards  will  bear 
submergence  for  thirty-live  and  even  forty  days,  deciduous 
orchards  about  three  weeks;  but  when  in  the  growing  condi- 
tion, injury  is  suffered  much  more  quickly. 

It  follows  that  whenever  the  soil-pores  remain  completely 
filled  with  water  for  a  length  of  time,  there  is  danger  to  the 
welfare  of  nearly  all  plants  commonly  cultivated  in  the  tem- 
perate zones.  It  is  therefore  important  to  know  how  much 


202  SOILS. 

water  will  bring  about  this  undesirable  condition  in  the  dif- 
ferent kinds  of  soil. 

To  determine  this  point  we  may  either  employ  the  deter- 
mination of  pore  space  by  a  comparison  of  the  density  of  the 
soil  constituents  (see  chap.  7,  p.  107)  with  the  volume  weight 
of  the  soil;  or  we  may  measure  directly  the  amount  of  water 
required  to  fill  the  pore-space.  For  the  latter  purpose  it  is 
only  necessary  to  measure  the  amount  of  water  (conveniently 
flowing  from  a  graduated  pipette)  which,  rising  slowly  from 
below  in  a  U-shaped  tube  so  as  to  expel  all  the  air  before  it, 
is  required  to  fill  a  definite  weight  or  volume  of  the  soil  en- 
tirely full,  so  as  to  rise  to  its  surface.  We  thus  ascertain  the 
amount  of  empty  space  existing  within  the  soil,1  which  in  the 
absence  of  water  will  ordinarily  be  filled  by  air. 

In  most  cultivated  soils,  as  already  stated,  the  air-space  con- 
stitutes about  25%  to  50%  of  their  volume;  and  this  space 
when  filled  with  water  represents  what  is  commonly  termed 
their  maximum  water  capacity  or  saturation  point.  It  is  of  in- 
terest to  know  this,  because  it  has  been  ascertained  from  ex- 
perience that  in  order  that  plants  may  reach  their  best  develop- 
ment, the  capillary  water  present  should  not  amount  to  more 
than  60%,  or  less  than  40%  of  its  maximum  water-holding 
capacity;  thus  leaving  about  half  the  pore-space  filled  with  air. 
This  optimum,  however,  varies  somewhat  for  different  plants, 
some,  like  celery,  being  more  tolerant  of  excess,  and  others 
being  more  tolerant  of  a  deficiency  of  moisture,  as  is  the,  e.  g., 
egg-plant,  originally  a  desert  growth. 

Capillary  Ascent  of  Water  in  Soil  Columns. — When  a  col- 
umn of  dry  soil  (e.  g.,  contained  in  a  glass  tube  closed  with 
muslin  at  the  lower  end)  is  brought  in  contact  with  water,  the 
latter  is  soon  seen  to  ascend  in  the  soil,  wetting  it  and  thus 
changing  its  color  so  as  to  permit  of  ready  observation  of  its 
progress.  At  first  the  rise  is  comparatively  rapid,  in  some 
cases  as  much  as  an  inch  in  one  minute;  but  it  soon  slows 
down  and  after  a  time  ranging  from  a  few  days  to  many 

1  Simple  as  this  operation  appears  to  be,  it  is  found  to  be  by  no  means  easy  to 
expel  with  certainty  every  small  air  bubble  without  resorting  to  means  which 
would  destroy  the  natural  condition  of  the  soil ;  such  as  boiling,  or  the  use  of  the 
air-pump.  These  determinations  cannot  therefore  lay  claim  to  gieat  accuracy. 


THE  WATER  OF  SOILS. 


203 


months,  reaches  a  maximum  height  beyond  which  the  liquid 
water  will  not  rise.  The  ascent  is  most  rapid,  and  stops 
soonest,  in  coarse  sandy  soils;  it  rises  most  slowly,  but 
in  the  end  considerably  higher,  in  heavy  clay  soils. 
The  most  rapid  continuous  rise,  and  ultimately  the  highest, 
occurs  in  salty  soils  containing  but  a  small  propor- 
tion of  clay.  The  maximum  height  of  capillary  rise 
thus  far  observed,  viz.  10.17  feet,  was  noted  in  the  case  of 
quartz  tailings  from  a  stamp  mill,  ranging  from  .005  mm.  to 
.016  mm.  in  diameter;  but  it  took  about  18  months'  time  to 
reach  this  maximum.  The  excessively  fine  texture  of  clay 
opposes  great  frictional  resistance  to  the  movement  of  the 
water,  and  the  same  is  true  of  the  finest  silts,  which,  like  clay, 
remain  almost  indefinitely  suspended  in  water.  But  it  must  be 
remembered  that  while  pure  grains  of  silt  will  in  wetting  re- 
main unchanged  in  size,  clay  particles,  and  the  clay  incrusting 
silt  grains,  will  on  wetting  swell  greatly,  and  thus  fill  up  the 
interstices,  largely  closing  them  up  against  the  passage  of 
water. 

These  facts  are  exemplified  and  graphically  illustrated  below. 

The  soils  selected  for  this  illustration,  from  California  lo- 
calities, are  the  following: 

No.  233.  Very  sandy  soil  from  near  Morano,  Stanislaus 
County.  Typical  of  the  noted  wheat-growing  region  of  the 
lower  San  Joaquin  Valley,  from  northern  Merced  to  Southern 
San  Joaquin  Counties ;  bench  or  plains  lands.  First  foot. 

No.  1197.  Sandy  alluvial  soil  from  near  the  confluence  of 
the  Gila  and  Colorado  rivers,  near  Yuma.  Very  deep,  light 
and  easily  cultivated.  First  foot,  but  almost  identical  to  15 
feet. 

No.  168.  Silty  alluvial  soil  from  the  old  alluvium  of  the 
Santa  Clara  River,  near  Santa  Paula,  Ventura  County.  Very 
deep,  very  easily  tilled ;  a  typical  alluvial  loam  of  the  arid 
region. 

No.  1697.  Black  adobe  or  clay  soil,  from  the  experiment 
station  grounds,  Berkeley.  A  heavy  clay  soil,  originally  a 
swamp  deposit,  becoming  very  tenacious  when  wet.  An  ex- 
cellent wheat  soil. 

The  physical  analyses  of  these  soils  are  given  below. 


204 


SOILS. 

PHYSICAL  ANALYSES  OF  TYPICAL  SOILS. 


Si 

It. 

Sand, 

Clay. 

Fine, 

Coarse, 

2.0  to 
64  mm. 

<.25  to 

.510  2.  mm. 

h.  v. 

•  5mm.  h.  v. 

h.  v. 

No.    233. 

Morano  sandy  soil  

2.82 

T  O7 

-!  40 

802  5 

No.  1  197. 

Gila  bottom  soil  

"?  21 

c  c-i 

I  C  42 

72  O1 

No.    198. 

Ventura  silty  soil  

1  5  02 

I  C  24 

2i;84 

4C  41 

No.  1697. 

Berkeley  adobe  soil  .... 

44.27 

25-35 

1347 

'3-37 

The  most  striking  feature  in  this  diagram  is  the  very  rapid  1 
and  high  ascent  in  the  combination  of  sediments  represented 
by  the  Gila  bottom  soil.  It  outstrips  at  once  both  the  sandy 
soil  from  Stanislaus,  which  contains  a  trifle  less  of  clay,  and 
the  silt  soil  from  Ventura,  from  which  at  first  sight  it  does  not 
seem  to  differ  widely,  but  which  contains  considerably  more 
clay.  It  is  doubtless  the  latter  which  so  greatly  retards  the 
motion  of  the  water,  as  is  still  farther  seen  in  the  case  of  the 
clay  or  adobe  soil.  It  will  be  noted  that  on  the  second  and 
third  days,  the  Gila  soil  had  raised  the  water  nearly  twice  as 
high  as  the  adobe,  and  that  it  took  only  18  hours  to  raise  it 
nearly  the  same  height  as  that  attained  by  the  Ventura  silt  in 
so  many  days.  But  it  ceased  to  rise  after  the  1251!!  day, 
while  the  Ventura  soil,  continuing  for  195  days,  finally  rose 
3  inches  higher.  The  adobe  also  continued  its  rise,  but  did  not 
reach  the  same  height  as  the  Gila  soil  by  nearly  two  inches. 
There  can  be  no  doubt  that  the  energetic  and  high  rise  of  the 
latter  proves  an  important  factor  in  the  culture  of  these  lands. 

The  coarse  sandy  soil  reached  its  highest  limit,  i6l/2  inches, 
within  six  days,  when  the  silty  Gila  soil  stood  at  about  double 
that  height. 

Ascent  of  Water  in  uniform  2  Sediments. — Loughridge  has 
ascertained  the  rate  of  ascent  of  uniform  sediments  of  differ- 
ent grain-diameters,  with  the  results  shown  in  the  diagram 

1  The  ascent  is  of  course  most  rapid,  in  the  large  tubes  almost  instantaneous, 
when    the    capillary  space  is   entirely  clear ;  but    in  the  complex  system  of  con- 
nected air  spaces  in  soils,  the  curved   paths  and   the  friction  obstruct  the  move- 
ment. 

2  I.  e.,  uniform  between  the  narrow  limits  given. 


THE  WATER  OF  SOILS. 


205 


186  n*W 


FIG.  3$. — Columns  showing  heights  to  which   water   will   rise  by  capillarity  in  soils  of   different 
physical  composition,  and  rates  of  ascent. 


2O6 


SOILS. 


0 


Q 


0 


0 


I) 


Q 


I) 


c 


u 


1  1  i  I  !  !  !  k! 


iHj 


m 


N:  :  i 
:§:  i  i 


!    {^v 

&4*- 


:^r« 

!§!§ 


pmr;flT 


•—  Q 


12mm. 

5onds 


THE  WATER  OF  SOILS.  20; 

subjoined,  together  with  the  maximum  height  reached  by  each. 
The  diagram  is  very  eloquently  illustrative  of  the  great  differ- 
ences in  the  capillary  properties  of  granular  sediments  of  the 
various  grades ;  and  it  would  seem  that  it  ought  to  be  possible 
to  deduce  from  it  by  a  somewhat  complex  formula  the  rate 
and  height  of  ascent  of  water  in  any  soil  of  known  physical 
composition.  In  nature,  however,  the  presence  of  clay  and 
the  greater  or  less  degree  of  flocculation  of  mixed  sediments 
will  always  vitiate  to  a  very  great  extent  the  results  deducible 
from  such  calculations ;  hence  the  data  conveyed  by  the  observ- 
ations of  Loughridge  must  be  considered  applicable  only  to 
granular  sediments  free  from  clay  and  entirely  deflocculated. 

It  is  curious  that  in  this  case  the  "  clay  "  showed  a  rise 
markedly  below  that  of  the  finest  granular  sediment,  despite 
the  extreme  fineness  of  its  particles.  This  proves  plainly  that 
the  physical  nature  of  colloid  clay  is  unlike  that  of  the  granular 
sediments ;  as  has  been  repeatedly  mentioned  above. 

Maximum  and  Minimum  of  Water-holding  Power. — It  is 
clear  that  at  the  base  of  the  columns  of  soils  just  considered, 
the  maximum  of  water-absorption  of  which  the  soil  is  capable 
will  have  been  brought  about;  while  at  the  top  of  the  same 
column,  the  minimum  of  possible  liquid  absorption  (continu- 
ous films  of  water)  will  exist.  The  same  minimum  moisture- 
condition  will  be  produced  when  a  limited  quantity  of  water  is 
placed  with  a  large  mass  of  soil ;  the  moisture  will  spread  to 
certain  limits,  until  the  surface  films  of  water  have  all  acquired 
uniform  tension ;  and  will  then  cease  to  extend,  except  by 
evaporation  and  hygroscopic  absorption.1  It  is  clear  that  the 
same  condition  will  be  brought  about  in  the  course  of  time  at 
the  top  of  a  soil  column  in  which  water  has  percolated  from 
above;  and  hence  the  minimum  mentioned,  aside  from  evapora- 
tion, represents  approximately  the  usual  condition  of  the  soil 

1  Ad.  Mayer  ( Agriculturchemie  2,  p.  141)  designates  this  minimum  content  of 
liquid  water  as  the  "  absolute  "  water  capacity  of  the  same  ;  but  it  is  not  obvious 
wherein  this  factor  is  better  entitled  to  this  name  than  would  be  the  maximum 
(see  Wollny's  Forsch.,  1892,  p.  i.).  M.  Whitney  (Rep.  Proceedings  Ass'n  Agr.  Coll. 
&  Kxp't  St'ns,  Nov.  190.})  gives  as  a  new  observation  the  fact  that  in  soils  ap- 
proaching the  drought  condition  water  "  does  not  obey  the  ordinary  physical  laws 
as  we  recognize  them  in  capillarity."  This  evidently  refers  simply  to  the  well- 
known  phenomenon  mentioned  above. 


208 


SOILS. 


near  the  surface  within  a  variable  time  after  a  rain,  or  irriga- 
tion, when  the  descending  water  column  has  attained  a  length 
corresponding  to  the  height  to  which  the  water  would  have 
risen  from  below  in  a  tube  arranged  as  shown  on  p.  205.  It 
is  therefore  a  condition  of  very  frequent  occurrence  in  the  arid 
region. 

Capillary  Water  held  at  Different  Heights  in  a  Soil  Col- 
umn.— To  determine  the  amounts  of  water  held  in  the  differ- 
ent portions  in  columns  of  soils  in  which  water  ascends  by 
capillary  rise,  the  following  plan  was  adopted  by  the  writer  in 
collaboration  with  Loughridge  (Rep.  Calif.  Sta.  1892-4,  p. 

99). 

Instead  of  glass  tubes  the  soils  to  be  tested  were  placed  in 

copper  tubes  one  inch  in  diameter,  divided  into  segments  six 
inches  long,  and  flattened  on  one  side.  In  the  flattened  side  a 
slot  half  an  inch  wide  was  left,  and  glass  plates,  held  in  posi- 
tion by  rubber  elastics,  were  cemented  on  the  slotted  side  by 
means  of  paraffin,  to  prevent  a  sifting-out  of  the  soil.  The 
short  sections  can  be  connected  at  Uie  ends  like  joints  of  stove- 
pipe, and  the  earths  can  be  easily  introduced  in  proper,  even 
condition.  It  was  thus  possible  to  gain  access  to  any  portion 
of  the  column  at  any  time,  for  the  taking  of  samples. 

WATER  CONTENTS  OF  SOIL  COLUMNS   AT  VARIOUS   HEIGHTS  ABOVE  WATER    LEVEL. 


No. 

233 

"97 

1679 

Height  above  Water 
Level. 

Sandy  Soil, 
Morano. 

Sandy  Alluvium, 
Gila. 

Adobe,  Berkeley. 

47  inches 

4-33 

42  inches 

10.26 

36  inches 

11.99 

30  inches 
24  inches 

15.26 
21.39 

10.26  • 

18  inches 

27.63 

29.48 

12  inches 

3-93 

32.48 

33-04 

6  inches 

14.15 

35-°4 

38.47 

3  inches 

38-49 

i  inch 

24-34 

36.64 

44.41 

Since  gravity  limits  the  capillary  ascent  in  a  progressive   ratio,  as 
shown   in   diagram    39,  it  is  obvious  that   the  true  maximum  saturation 

1  This  figure  represents  only  a  temporary  condition ;  the  full  height  of  46  inches 
was  not  reached  until  the  I95th  day. 


THE  WATER  OF  SOILS. 


209 


can  exist  only  in  a  very  short  (strictly  speaking,  an  infinitesimally 
short)  vertical  column.  The  least  practicable  height  for  experimental 
work  being  about  i  cm.  (|  in.),  the  writer  has  adopted  for  the  purpose 
of  rapid  determination  of  this  factor,  the  use  of  a  brass  cylinder  i  cm. 
high  and  of  such  width  as  to  contain,  for  the  sake  of  convenience,  25 
or  50  cm.  of  soil.  This  cylinder  has  a  finely  perforated  bottom,  which 
may  be  covered  with  filter  paper ;  after  being  filled  with  soil  which  ha° 
been  struck  level,  and  weighing,  it  is  immersed  to  i  mm.  depth  in  dis- 
tilled water  and  allowed  to  rest  for  an  hour ;  then  quickly  dried  outside 
and  beneath  with  filter  paper,  and  again  weighed.  The  amount  of 
water  found  by  difference  should  for  all  practical  purposes  be  referred 
to  the  volume,  not  to  the  weight,  of  the  soil,  so  as  to  eliminate  the 
error  arising  from  the  varying  specific  gravity  of  the  latter. 

In  most  cases  the  surface  of  the  soil  in  the  sieve  cylinder  remains 
level  after  wetting ;  but  sometimes  it  swells  so  as  to  rise  above  its  dry 
level,  even  to  the  extent  of  nearly  30%  (see  chapter  7,  p.  114). 
This  happens  especially  in  strongly  ferruginous  soils.  In  the  case  of 
"black  alkali"  soils,  in  wetting  an  enormous  collapse  sometimes  takes 
place  (see  chapter  22). 

If  it  be  desired  to  determine  also  the  minimum  liquid  absorption 
(see  below),  the  surface  of  the  wet  soil  is  first  covered  with  air-dry  soil, 
to  absorb  the  surplus  moisture,  and  finally  with  soil  previously  saturated 
with  hygroscopic  moisture  ;  the  added  soil  being  each  time  thrown  off 
and  finally  the  surface  "  struck  "  level  with  a  tense  silk  thread  before 
weighing.  Corrections  must  be  applied  for  the  usual  increase  in 
weight,  from  the  addition  of  soil,  and  for  the  hygroscopic  moisture. 

While  the  minimum  of  liquid  absorption  can  thus  be  deter- 
mined quickly,  without  awaiting"  the  capillary  ascent  of  a  water 
column,  and  if  sufficient  time  is  given  can  also  lie  determined 
in  higher  columns,  as  proposed  by  Mayer  (XYollny's  Forsch. 
Vol.  3),  the  maximum  cannot  thus  be  determined  without 
gross  inaccuracy.  In  determinations  made  by  the  writer  it 
was  found  that  (lie  figures  for  the  minima  of  very  different 
soils  (clayey  and  sandy)  of  the  arid  region,  differ  proportion- 
ally much  less  than  do  ihe  respective  maxima.  In  few  of 
these  soils  it  was  found  to  exceed  about  10  per  cent,  and  it 
scarcely  fell  below  4  per  cent  even  in  very  sandy  soils.  A 
very  deep,  sandy  soil,  which  had  been  irrigated  in  May,  and 
14 


210  SOILS. 

upon  which  no  rain  had  since  fallen,  showed  in  July  in  the 
second  foot,  upon  which  rested  ten  inches  of  fully  air-dried  soil 
free  from  vegetation,  a  water-percentage  of  eight  per  cent.1 

Capillary  Action  in  Moist  Soils. — In  the  preceding  discus- 
sion the  case  of  columns  of  air-dry  soils,  so  common  in  the 
arid  regions,  has  been  considered.  It  is  obvious  that  a  soil 
column  holding  the  minimum  of  capillary  water  may  be  of 
any  height;  so  that  when,  as  happens  in  the  open  field,  the 
rain  water  soaks  down  beyond  the  range  of  capillary  rise  in  a 
given  soil,  the  upper  portions  of  the  latter,  above  that  range, 
will  remain  at  the  minimum  of  moisture-content  so  long  as  it 
is  not  depleted  by  evaporation.  King  has  made  extended 
observations  on  soil  columns  ten  feet  high  and  moistened 
throughout  the  mass.  Capillary  movement  takes  place  in 
moist  soils  much  more  rapidly  than  in  dry  ones,  although 
when  sufficient  time  is  given  the  final  adjustment  will  of 
course  be  the  same.  King's  experiments  showed  that  evapor- 
ation at  the  surface  of  the  tenfoot  columns  caused  a  sensible 
depletion  of  the  water  content  originally  existing  at  the  depth 
of  ten  feet,  in  the  course  of  314  days.  While  so  slow  a 
movement  might  not  be  of  any  benefit  during  the  growth- 
period  of  shallow-rooted  annual  crops,  the  fact  shown  is  of 
importance  to  permanent  plantings,  as  of  trees  and  vines. 

Another  and  not  so  readily  intelligible  effect  observed  by 
King  is  that  when  the  surface-soil  is  wetted,  moisture  may  be 
withdrawn  toward  the  surface  from  the  lower  layers.  In  one 
experiment  he  found  that  when  water  was  applied  on  the  sur- 
face so  as  to  add  two  pounds  of  water  to  each  surface  foot  in 
several  soils,  at  the  end  of  26  hours  there  had  been  an  increase 
of  three  pounds  in  the  same,  and  a  loss  of  one  and  three  quarter 
pounds  from  the  second  and  third  feet.  The  cause  of  this 
translocation  is  probably  a  "  distillation  "  of  the  subsoil  mois- 
ture toward  the  cooled  soil ;  the  fact  that  it  occurs  is  of  prac- 
tical interest,  since  it  seems  to  show  that  wetting  the  upper 

1  Hall  (The  Soil,  p.  66)  gives  for  the  minima  in  the  case  of  soils  examined  by 
him  the  following  figures  :  coarse  sandy  soil,  22.2,  light  loam,  35.4,  stiff  clay,  45.6, 
sandy  peat,  52.8.  These  figures  are  very  much  higher  than  for  apparently  similar 
materials  used  by  the  writer,  and  the  differences  exceed  those  between  the 
maxima  given  for  the  same.  This  discrepancy  I  am  unable  to  account  for. 


THE  WATER  OF  SOILS. 


211 


portion  of  the  soil  by  cold  rain  or  irrigation  may  tend  to  raise 
additional  supplies  from  below.  At  the  change  of  seasons  we 
not  uncommonly  find,  in  digging  tree  holes  or  wells,  a  wet 
streak  at  from  9  to  18  inches  below  the  surface,  caused  evi- 
dently by  the  condensation  of  subsoil  moisture,  at  the  limit  of 
a  cold  zone  resulting  from  the  penetration  of  unseasonable  tem- 
perature ("cold  snap")  from  above.  Such  movements  of 
soil-moisture  by  means  of  evaporation  and  recondensation 
within  the  soil  can  of  course  take  place  even  when  the  mini' 
mum  of  liquid  absorption  has  been  reached  and  direct  capil- 
lary movement  has  ceased.  It  is,  as  it  were,  dew  within  the 
soil. 

Proportion  of  Moisture  Available  to  Growing  Plants. — Not 
all  the  capillary  moisture  contained  in  soils  is  available  to 
plants,  as  can  readily  be  seen  from  the  fact  that  many  plants, 
especially  when  growing  in  pots,  begin  to  wilt  while  the  soil 
still  appears  visibly  moist.  The  limit  of  wilting  differs  greatly 
in  different  plants,  and  in  the  open  ground  it  is  difficult  to  as- 
certain that  limit,  because  the  deeper  roots  continue  to  supply 
moisture  from  moister  substrata.  Hence  potted  plants  wilt 
while  the  soil  appears  much  moister  than  when  the  same  grow 
in  the  field.  King  l  has  determined  the  amounts  of  moisture 
down  to  43  inches  in  a  Wisconsin  soil  in  which  clover  and  corn 
were  at  the  wilting  point,  as  in  the  following  condensed  table : 


Clover. 

Maize. 

Fallow 
ground. 

First  1  2  inches,  clay  loam  

8.44 

7  01 

17  or 

Second  12  inches,  reddish  clay  

12.84 

I  I  7O 

1986 

24  to  30  inches,  sandy  clay  

I  -i  C2 

10  84 

18  56 

40  to  43  inches,  sand  

Q  ^1 

A  17 

I  C  GO 

It  is  plainly  shown  here  that  the  roots  of  clover  and  corn 
were  unable  to  utilize  the  higher  moisture-content  of  the  sub- 
soil-clay to  the  same  extent  as  the  smaller  amounts  present  in 
the  surface  foot,  and  in  the  sandy  substrata.  Evidently  the 
moisture  in  the  clay  soil  was  more  tenaciously  retained. 


Physics  of  Agriculture,  p.  135. 


212  SOILS. 

This  is  doubtless  due,  as  King  shows,  to  the  equal  thinness 
of  the  moisture  film  remaining  on  the  soil  grains  in  either 
case;  the  number  of  grains,  and  therefore  the  aggregate  sur- 
face holding  these  films,  being  much  greater  in  the  clay  than  in 
sands ;  hence  the  higher  water  content. 

It  is  interesting  to  compare  these  figures  given  by  King  for 
clover  and  maize  at  the  wilting-point,  and  fallow  ground  adja- 
cent, with  those  given  by  Eckart  ( Rep.  Expt.  Sta.  Haw.  Sugar 
Planters'  Ass'n.,  1903)  for  those  affording  good  growing 
conditions  for  sugar  cane  on  the  (highly  ferruginous)  soils 
of  that  station.  The  plots  were  irrigated  at  the  rate  of  one, 
two  and  three  inches  of  water  per  week,  allowance  being 
made  for  the  rainfall.  Two  inches  proved,  on  the  whole,  to 
give  the  best  average  results  for  production.  The  moisture 
determination  of  the  soil  under  the  two-inch  regime  gave  an 
average  moisture  content  of  29.13%  in  the  first  foot  of  soil. 
It  is  not  stated  what  was  the  hygroscopic  coefficient  of  that 
soil,  but  it  was  probably  very  high;  in  the  neighborhood  of 
2I-5%»  Judging  by  the  determinations  made  with  six 
Hawaiian  soils  at  the  California  Station.  This  would  indi- 
cate about  7.63%  of  free  moisture  as  the  optimum  for  sugar 
cane. 

Moisture-requirements  of  Crops  in  the  Arid  Region. — 
Plants  (particularly  broad-leaved  ones)  which  have  made  a 
brash  growth  during  a  period  of  abundant  moisture,  will  wilt 
quickly  when  sunshine  returns,  and  take  some  time  to  adapt 
themselves  to  the  drier  conditions.  On  the  other  hand,  plants 
accustomed  to  dry  air  and  scanty  soil-moisture,  will  not  wilt  or 
suffer  under  what  would  elsewhere  be  considered  very  rigorous 
conditions.  Loughridge  *  has  made  numerous  determinations 
of  moisture  in  soils  in  which  crops  were  beginning  to  suffer, 
and  others  on  similar  soils  that  were  growing  normally,  and 
found  that  in  general,  not  only  were  the  differences  in  mois- 
ture content  considerably  less  than  in  the  case  above  quoted 
from  King's  observations,  but  that  the  amounts  of  free  mois- 
ture required  by  various  crops  in  the  arid  climate  of  Cali- 
fornia were  surprisingly  small. 

The  tables  below  show  the  results  of  observations  made  by 

1  Rept.  Cal.  Expt.  Sta.  1897-08,  pp.  65-96. 


THE  WATER  OF  SOILS. 


2I3 


Loughridge  during  several  drought  years  in  California;  so  ar- 
ranged as  to  show  the  differences  of  moisture  content  for  the 
same  crop  in  different  soils.  It  will  be  observed  that  in  all 
cases  where  a  crop  growing  on  a  clay  soil  could  be  compared 
with  the  same  on  a  lighter  soil,  the  moisture  required  to  keep 
the  crop  in  good  condition  was  very  much  greater  in  the  clay 
than  in  the  loam  or  sandy  soils.  In  the  case  of  apples,  e.  g., 
8.3%  of  water  was  abundant  to  keep  the  trees  in  excellent  con- 
dition on  a  loam  soil,  while  on  a  clay  soil  holding  12.390  the 
condition  was  very  poor.  That  this  difference  is  due  in  the 
main  to  the  difference  in  the  hygroscopic-moisture  coefficient 
of  the  respective  soils,  is  plainly  apparent  in  several  cases.  It 
is  therefore  not  the  total  moisture  content,  but  the  free  mois- 
ture present  in  excess  of  what  is  held  by  hygroscopic  absorp- 
tion, that  determines  the  welfare  of  the  plant. 

By  determining,  first,  the  total  moisture  in  the  soils,  as  taken 
in  the  field,  then,  after  allowing  them  to  become  air-dry,  deter- 
mining the  maximum  of  hygroscopic  moisture  they  would  ab- 
sorb (see  p.  198),  Loughridge  found  by  difference  the  amount 
of  free  moisture,  or  liquid  water  which  must  be  present  in  the 
soil  to  prevent  the  crops  from  suffering.  An  exceptionally 
good  opportunity  for  these  observations  was  offered  by  the 
dry  season  of  1898,  during  which  crops  suffering  and  not 
suffering,  on  identical  lands,  could  easily  be  found.  The  de- 
terminations were  always  made  for  each  foot  of  the  upper 
four  feet  of  the  land  in  the  immediate  neighborhood  of  the 
trees  or  among  the  field  crops.  The  first  table  exemplifies  the 
method  of  procedure;  the  second  gives  the  summary  of  results 
for  the  several  crops  and  trees,  as  calculated  from  observations 
made  during  the  season. 


214 


SOILS. 


TABLE  SHOWING  CONDITION  OF  CROPS  ON  VARIOUS  SOILS  UNDER 
DIFFERENT  MOISTURE-CONDITIONS. 


Kind  of  Crop. 

Kind  of  Soil. 

Condition  of 
Crop. 

Per  cent  Moisture  in  four  feet. 

Total. 

Hygro- 
scopic. 

Free. 

Tons 
per 
acre. 

Wheat  

Very  sandy  
Sandy  loam  .... 
Clay  
Clay  adobe  

Poor  
Good  
Dead  
Very  good  

2.6 
12.8 

14.1 
12.9 
6.1 
10.7 
12.4 

8-5 
1.9 

8-5 
7-9 

8-3 
12.3 

6-3 
6.9 

S-2 
8.6 

5-2 
J'9 

8.2 

6.8 

II.  2 
6.4 
6-3 

3-i 

li 

5.6 

10.5 
8.8 

2-3 
8.8 
5.6 
5.0 

6.1 
6.9 

5-5 
10.8 

3-3 
S-o 
3-8 
8.6 

3-8 
1.9 

5.0 

5-o 
9.0 

5-4 
3-1 

2-4 

•7 

7.2 

3-6 
4-i 
3-8 
1.9 
6.8 

3-5 
•4 
1.9 

I.O 

2.8 

i-5 

3-o 
1.9 
1.4 
o 

1.4 

o 

3-2 
1.8 

2.2 
I.O 

3-2 
•7 

56 
576 
288 
328 

3°4 
152 

544 
280 

£ 

80 
224 

120 
24O 
152 
112 
O 
112 
0 
256 
144 
I76 
80 
256 
S^ 

K 

« 
Maize  

Sandy  loam  .... 
Black   adobe  .  .  . 
Black  loam  

Fair  
Wilting  

Barley  

Sugar  Beets.  .  .  . 
Vines  

Good  

Loam     .... 

Good 

Sandy  loam  .... 
Loam  

Poor  
Good  , 

Almonds  

Same  field  

Suffering  

Loam  

Excellent  

u 

Apricots  

Clay  
Loam  

Poor  
Excellent     .... 

Gravelly  loam.  . 
Red  loam  

Poor  
Good  

Fies  .  . 

Heavy  loam...  . 
Red  loam 

Wilting  

Olives  

Good 

Sandy  loam  .... 
Red  loam  

Suffering  .. 

Peaches  

Good  

u 

Gray  loam  

u 

Poor  
Excellent  

Prunes  

Poor  

Citrus  fruits...  . 
i<           « 

Sandy  loam.  .  .  . 

Good  

Sandy  soil  

Leafless  

TABLE  SHOWING  DROUGHT-ENDURANCE  OF  VARIOUS  CROPS  IN  ARID 

REGION. 


Free  water  in  four 

feet  of  soil. 

Crops  that  did  well  in  lowest 

Crops  that  suffered  in  highest 

TV»nc 

amount  of  moisture  men- 
tioned in  first  column. 

amount  or  moisture  men- 
tioned in  first  column. 

Percent. 

l  Olio 

per  acre. 

o    to  i.o 

80    j 

Apricots,  Olives,  Grapes, 
Peaches,  Soy-bean. 

Citrus,  Pears,  Plums,  Acacia. 

I.o  to  1.5 

120 

Citrus,  Figs. 

Almonds,  Apples. 

1.5  to  2. 

160 

Almonds,  Plums,  Saltbush. 

Barley. 

(  176 

Prunes. 

2    to  2.5 

i      ' 

\      2OO 

Walnuts,  Eucalyptus. 

Prunes. 

2-5  to    3 

224 

Apples. 

3    to  3.5 

288 

Pears. 

3   to    4 

322 

Hairy  Vetch. 

Wheat. 

4   to    5 

4OO 

Wheat,  Maize. 

5   to   6 

480 

Sugar  beets,  Sorghum. 

Sugar  beets. 

CHAPTER  XII. 

THE  WATER  OF  SOILS.— Continued. 

SURFACE,    HYDROSTATIC   AND  GROUND   WATER  ;   PERCOLATION. 

SINCE  all  the  water  of  soils  and  plants  is  directly  or  indi- 
rectly derived  from  the  rainfall  (including  therein  snow  and 
hail),  some  general  points  regarding  this  factor  require  first 
consideration.  While  it  is  not  the  object  of  this  work  to  dis- 
cuss climatology  in  detail,  yet  the  times  of  the  year  and  the 
manner  in  which  precipitation  comes,  acts  upon  and  is  disposed 
of  in  the  soil  under  different  climatic  conditions,  must  of  neces- 
sity form  an  essential  part  of  its  subject  matter. 

Amount  of  rainfall. — The  rain  falling  in  the  course  of  a 
year  is  usually  stated  in  the  form  of  "  inches  "  (or  centime- 
ters), implying  the  height  of  the  water  column  that  would  be 
shown  at  the  end  of  the  year  had  it  all  been  allowed  to  accu- 
mulate; or,  the  sum  of  all  the  successive  rains  (including 
snow)  observed  during  the  year.  Since  this  amount  ranges 
all  the  way  from  nothing,  or  a  mere  fraction  of  an  inch  (as  in 
portions  of  the  Andes,  and  of  the  great  African  and  Asian 
deserts)  to  as  much  as  600  inches  or  fifty  feet  (Cherapundji 
in  eastern  India),  the  adaptation  of  agricultural  practice  to  the 
maintenance  of  the  proper  moisture-supply  to  crops  is  largely 
a  local  question,  oftentimes  of  not  inconsiderable  difficulty. 
This  is  especially  the  case  where  torrential  rains,  yielding  sev- 
eral inches  of  rain  in  a  few  hours,  alternate  with  light,  soaking 
rainfall,  as  is  very  commonly  the  case  in  the  interior  of  con- 
tinents, and  more  especially  in  the  United  States  east  of  the 
Rocky  Mountains.  Westward  of  the  same  the  rainfall  de- 
creases so  rapidly  that  at  or  about  the  one-hundredth  meridian 
(the  longitude  of  Bismark  and  Pierre,  Dakota,  and  Dodge  City, 
Kansas)  we  already  reach  the  annual  average  of  20  inches, 
which  is  commonly  assumed  to  l>e  the  limit  below  which  crops 
cannot  safely  be  grown  without  irrigation.  The  "  cloud- 

215 


2l6  SOILS. 

bursts  "  occasionally  occurring  within  these  limits  are  usually 
confined  to  mountainous  regions,  and  the  water  they  pour 
down  on  the  dry  soil  is  rarely  of  any  direct  benefit  to  agricul- 
ture; hence  they  cannot  be  properly  counted  in  the  general 
estimate  of  the  effective  rainfall.  A  region  of  high  rainfall 
(up  to  100  inches  and  over),  however,  extends  along  the  Pa- 
cific coast  from  northern  California  through  western  Oregon 
and  Washington  across  British  Columbia  to  Alaska,  to  sea- 
ward of  the  Sierra  Nevada,  Cascade,  and  Alaskan  coast  ranges. 

In  the  country  east  of  the  Mississippi  river,  the  average  an- 
nual rainfall  ranges  from  30  inches  in  the  region  of  the  Great 
Lakes,  and  45  to  50  inches  on  the  north  Atlantic  coast,  to  60 
inches  in  Louisiana  and  up  to  eighty  in  southern  Florida.  The 
average  of  the  Mississippi  Valley  and  Atlantic  coast  States  is 
usually  stated  at  about  45  inches,  which  is  distributed  more  or 
less  evenly  throughout  the  year,  excepting  usually  from  six 
to  eight  weeks  of  more  scanty  precipitation  in  the  latter  part 
of  August  and  in  September — the  "  Indian  summer"  season; 
so  that  the  winter  is  the  season  of  greatest  total  rainfall. 

Natural  disposition  of  the  Rain  Water. — The  rainfall  is 
naturally  first  disposed  of  in  two  ways,  viz.,  a  portion  which 
is  absorbed  by  the  soil,  and  another  which  is  at  once  shed  from 
the  surface  and  constitutes  the  "  surface  runoff."  The  portion 
absorbed  into  the  soil  is  subsequently  disposed  of  either  by 
soakage  downward  into  the  subdrainage  and  through  springs 
and  seepage  x  into  the  streams  and  rivers ;  or  by  evaporation. 
The  latter  again  occurs  in  two  different  ways,  viz.,  from  the 
soil-surface  itself,  or  through  the  roots  and  leaves  of  plants. 
The  importance  of  each  of  these  modes  is  sufficiently  great  to 
entitle  each  to  detailed  consideration. 

The  Surface  Runoff. — This  portion  of  the  disposal  of  rain 
may  range  all  the  way  from  nothing  to  almost  totality,  accord- 
ing to  the  nature  of  the  soil  and  the  condition  of  its  surface.2 

1  The  quiet  seepage  from  the  banks  and  beds  of  streams  plays  a  much  more  im- 
portant part  in  the  increase  of  volume  of  flow  than  is  commonly  supposed,  because 
unperceived   save  by  measurement  of  the   tributaries  and  comparison  with   the 
main  streams.     This  is  especially  true  of  the  drainage  in   the  arid  region,  where 
the  deep  and  pervious  soils  favor  diffuse  seepage  as  against  definite  spring  flow. 

2  Tourney  (Yearbook  U.  S.  Dep't  Agr.  1903)  states  that  in  the  San  Bernardino 
mountains  in  southern  California,  the  first  rainfall  (in  December)  was  absorbed  to 
the  extent  of  95°  0  in  forested   areas,  against   only  60°  0  in   the  non-forested ;  but 


THE  WATER  OF  SOILS.  217 

Sandy  soils,  especially  when  coarse,  may  absorb  instantly  even 
a  very  heavy  rainfall.  Heavy  clay  soils  when  dry  will  at  first 
also  absorb  quickly  quite  a  heavy  precipitation;  but  as  the 
beating-  of  the  raindrops  compacts  the  surface,  the  absorption 
quickly  slows  down,  so  that  heavy  downpours  of  brief  dura- 
tion, while  wetting  thoroughly  into  a  plastic  mass  the  first  two 
or  three  inches  of  a  clay  soil,  may  leave  all  beneath  dry,  to  be 
very  gradually  moistened  by  the  slow  downward  percolation 
against  the  resistance  of  the  air  in  the  soil;  while  the  greater 
part  of  the  later  portion  of  the  shower  will  drain  off  the  surface 
in  muddy  runlets.  Certain  soils  classed  as  loams,  having  the 
property  of  crusting  readily  by  rain  followed  by  sunshine  (see 
chapter  7,  p.  1 1 1  ),  in  heavy  showers  behave  hardly  better  than 
strong  clay  soils;  shedding  the  water  until  the  soaked  crust 
gives  way,  and  is  carried  off  in  muddy  streamlets.  Then  be- 
gins the  cutting-away  of  the  soil  that,  in  portions  of  the  Cotton 
States,  as  well  as  north  of  the  Ohio  river,  has  been  the  cause 
of  extensive  devastation  of  once  fruitful  culture  lands;  the  site 
of  which  is  now  marked  by  ''  red  washes  "  and  gullies  but  too 
familiar  to  the  eye  in  many  regions,  especially  of  the  southern 
United  States. 

Washing-away  and  Gullying  in  the  Cotton  States. — Nowhere  perhaps 
have  these  effects  been  so  severely  frit  as  in  portions  of  northwestern 
and  central  Mississippi,  and  this  case  is  so  instructive  as  to  deserve  a 
more  detailed  description.  In  the  regions  in  question  the  soil  stratum 
consists  of  a  yellow  or  brownish  loam  from  three  to  seven  feet  in 
original  thickness,  constituting  a  very  desirable  class  of  gently  rolling 
uplands,  which  at  one  time  claimed  to  be  the  best  cotton-growing 
portion  of  the  State.  It  was  originally  covered  with  an  open  forest  of 
oaks,  with  an  abundant  growth  of  grasses  that  afforded  excellent  pasture 
to  deer  and  cattle  ;  a  natural  park  gay  with  flowers  during  most  of  the 
season. 

When  these  lands  were  taken  into  cultivation  little  or  no  attention 
was  paid  to  the  direction  of  the  farrows  and  rows  of  corn  and  cotton  ; 

that  later,  after  the  soil  had  been  partially  saturated,  6o°'0  only  was  absorbed  in 
the  forested  land,  against  5°  0  in  the  non-forested.  While  it  is  generally  admitted 
that  forests  diminish  the  runol'f,  Rafter  (Relation  of  Rainfall  t<>  Runoff,  I".  S. 
Geol.  Survey  Paper,  No.  So,  p.  53)  contends  that  in  New  York  State  the  reverse  is 
true. 


218 


SOILS. 


most  commonly  the  plowing  was  done  "  up-hill  and  down,"  so  that  the 
"  dead-furrow  "  afforded  a  ready  opportunity  for  the  formation  of  washes 

cutting  into  the  subsoil,  during  the 

torrential  rains  sometimes  falling 
during  the  summers.  Even  when 
filled  with  soil  by  plowing,  these 
washes  would  frequently  re-open 
during  rains,  shedding  the  soil  in  a 
muddy  flood  upon  the  lower  lands. 
The  washing-away  of  the  surface 
soil,  thus  brought  about,  of  course 
diminished  the  production  of  the 
higher  lands,  which  were  then  com- 
monly "  turned  out  "  and  left  with- 
out cultivation  or  care  of  any  kind. 
The  crusted  surface  shed  the  rain 
water  into  the  old  furrows,  and  the 
FIG.  40.— Erosion  in  Mississippi  Table  Lands,  latter  were  quickly  deepened  and 

causing  destruction   of  agricultural  value   both  of       .  .  ,  .    .  ...  ,  1,1 

Uplands  and  Valleys.     (McGee,  «th  Ann.  Kept.    Widened  into  gullies— "red  Washes 

u.  s.,  1890-91.)  — whose   presence    rendered    any 

resumption  of  cultivation  difficult.  In  the  course  of  a  few  years  the 
soil-stratum  of  brown  loam  was  penetrated  into  the  loose  or  loosely 
cemented  sand  which  underlies  it  almost  everywhere,  and  is  very  readily 


FIG.  403. — Erosion  in  Mississippi  Table  Lands,  causing  destruction   of  agricultural  value  both   of 
Uplands  and  Valleys.     (McGee,  izth  Ann.  Kept.  U.  S.  G.  S.,  1890-91.) 

washed  away.     Soon  the  water,  gaining  yearly  in  volume,  undercut  the 
loam  stratum  so_as  to  cause  it  to  "cave"  into  gullies  in  huge  masses, 


THE  WATER  OF  SOILS. 


2I9 


which  with  the  sand  were  carried  into  the  valleys  adjacent,  filling  the 
beds  of  the  streams  so  as  to  cause  their  flow  to  disappear  under  the 
flood  of  sand.  As  the  evil  progressed,  large  areas  of  uplands  were 
denuded  completely  of  their  loam  or  culture  stratum,  leaving  nothing 
but  bare,  arid  sand,  wholly  useless  for  cultivation;  while  the  valleys  were 
little  better,  the  native  vegetation  having  been  destroyed  and  only 
hardy  weeds  finding  nourishment  on  the  sandy  surface. 

In  this  manner  whole  sections,  and  in  some  portions  of  the  State 
whole  townships  of  the  best  class  of  uplands  have  been  transformed 
into  sandy  wastes,  hardly  reclaimable  by  any  ordinary  means,  and 
wholly  changing  the  industrial  conditions  of  entire  counties  ;  whose 
county  seats  even  in  some  instances  had  to  be  changed,  the  old  town 
and  site  having,  by  the  same  destructive  agencies,  literally  "  gone  down 
hill."  This  destruction  of  lands  was  greatly  aggravated  by  the  civil 
war,  during  which,  and  for  some  time  after,  large  areas  of  lands  once 
under  cultivation  were  left  to  the  mercy  of  the  elements. 

Injury  in  the  arid  regions. — In  the  arid  regions,  where  the 
rainfall  frequently  comes  in  heavy  downpours  or  "  cloud- 
bursts," immense  damage  to  pasture  lands  has  been  brought 
about  by  overstocking,  in  Arizona  and  New  Mexico;  involving 
the  destruction  of  the  natural  cover  of  vegetation  and  the 
loosening  of  the  surface  especially  by  sheep;  after  which  a 
heavy  rainfall  will  carry  off  the  surface  soil,  the  muddy  water 
being  gathered  largely  in  the  trails  made  by  cattle  going  to 
water.  Thus  gradually  gullies  are  formed,  which  enlarging 
more  and  more  become  ravines  and  cut  up  the  pasture  slopes 
into  "  bad  lands,"  useless  equally  for  pasture  and  for  agricul- 
ture.1 California,  eastern  Oregon  and  Washington,  and  Mon- 
tana, offer  striking  and  lamentable  examples  of  the  same  de- 
structive agencies. 

Deforestation. — The  deforestation  of  hill  and  mountain 
lands  has,  the  world  over,  led  to  similar  results;  causing  not 
only  the  destruction  of  pasture  and  agricultural  lands,  but  also 
the  conversion  of  streams,  flowing  from  springs  and  seepage 
all  the  year,  into  periodic  torrents,  flooding  the  lowlands 
during  rains  by  the  rapid  running-off  of  the  water  from  the 
bare  and  hard-baked  mountain  slopes,  and  then  running  dry 

1  Open  Range  and  Irrigation  Farming.  R.  II  Forbes,  in  Forester,  N'os.  7,  9, 
1902. 


220  SOILS. 

within  a  short  time,  so  as  not  even  to  afford  drinking  water  to 
pasturing  cattle  in  summer.  Thus  for  half  a  century  the  un- 
solved problem  of  the  "  correction  of  the  waters  of  the  Jura 
mountains  "  was  before  the  Swiss  and  French  governments ; 
and  the  great  and  costly  public  work  involving  re-forestation, 
deflection  of  torrents  and  filling-in  of  deep  ravines  and  gullies, 
is  not  even  yet  nearly  completed.  In  Spain,  which  in  the  time 
of  the  Roman  occupation  was  largely  a  forest  country  with 
abundant  rainfall,  the  same  results  are  seen,  notably  in  the 
South,  in  the  wide,  and  mostly  dry,  sandy  beds  of  streams 
once  running  deep  and  clear ;  and  in  the  scarred  hill-and  moun- 
tain-sides, and  scant  vegetation  of  low  shrubs  ("  chaparral  ") 
that  replaces  the  once  abundant  tree  growth,  e.  g.,  in  Old  and 
New  Castile.  Unfortunately  the  lessons  taught  by  the  bitter 
experience  of  the  old  world  seem  to  require  actual  repetition 
in  the  new,  before  means  of  prevention  are  even  thought  of. 

Prevention  of  Injury  to  Cultivated  Lands  from  excessive 
Runoff. — The  fundamental  remedy  for  the  injurious  effects  of 
excessive  runoff  from  the  land  surface  is,  of  course,  to  facilitate 
its  absorption  into  the  soil  to  the  utmost  extent  possible,  by 
deep  tillage;  or  in  cases  where  this  is  undesirable  (as  when  in 
rainy  climates  excessive  leaching  of  the  land  is  feared),  to  so 
direct  and  control  the  surface  drainage  that  its  flow  shall  no- 
where be  so  rapid  as  to  carry  with  it  any  large  amounts  of 
earth,  or  to  wash  out  the  furrows.  To  this  end  its  fall  must  be 
diminished  by  "  circling,"  i.  e.,  plowing  nearly  at  right  angles 
to  the  slope  instead  of  up-and-down,  and  on  steep  slopes  especi- 
ally also  by  maintaining  open  furrows  or  ditches  having  a 
gentle  fall  only,  into  which  the  water  can  shed  and  flow  off 
quietly  in  case  the  furrows,  left  in  plowing,  prove  insufficient 
to  retain  and  shed  gradually  the  water  they  cannot  hold  per- 
manently. The  early  adoption  of  this  simple  expedient  would 
have  wholly  prevented  the  enormous  waste  of  fine  agricultural 
lands  referred  to  above. 

The  underdraining  of  lands  liable  to  washing  is  a  costly  but 
highly  effective  means  of  preventing  denudation;  and  the  lay- 
ing of  unclerdrains  in  gullies  already  formed,  to  prevent  farther 
deepening,  is  among  the  most  obvious  means  of  arresting 
farther  damage.  The  beneficial  effects  of  underdrainage  in 
conserving  moisture  will  be  discussed  farther  on. 


THE  WATER  OF  SOILS.  221 

ABSORPTION    AND    MOVEMENTS    OF    WATER    IN    SOILS. 

The  phenomena  and  laws  of  capillary  ascent  of  water  in 
soils,  as  discussed  in  the  preceding  chapter,  serve  best  to  de- 
monstrate the  general  behavior  of  liquid  water  within  differ- 
ent soils  and  their  several  grain-sizes ;  because  measurably  in- 
dependent of  the  physical  changes  that  almost  unavoidably  ac- 
company the  percolation  of  water  from  above  downward ; 
whether  such  water  comes  in  the  form  of  rain,  or  irrigation, 
or  even  when  applied  with  the  utmost  precautions  in  the  labor- 
atory. The  "  beating  "  of  rains  quickly  compacts  the  surface 
to  a  certain  extent,  varying  with  the  nature  of  the  soil,  its  con- 
dition of  more  or  less  perfect  tilth,  and  the  degree  of  violence 
with  which  the  rain  strikes  the  surface.  When  the  latter  has 
been  compacted  by  a  previous  rain  and  then  dried,  "  baking  " 
or  incrusting  the  surface,  the  latter  may  almost  wholly  shed  a 
rain  of  brief  duration,  which,  had  the  surface  been  loose,  would 
have  been  wholly  absorbed,  materially  benefiting  the  crop. 
Such  surface-crusting  is,  therefore,  injurious  in  preventing  the 
absorption  of  water  from  above;  and  in  addition,  it  serves  to 
waste,  by  evaporation,  the  moisture  contained  in  the  under- 
lying soil  and  subsoil.  For  the  crust  being  of  a  finer  (single- 
grain)  texture  than  the  tilled  portion  beneath,  it  will  forcibly 
abstract  from  the  latter,  by  absorption,  its  capillary  moisture, 
and  evaporating  it  at  the  upper  surface,  continue  to  deplete  the 
land,  to  the  great  injury  of  crop  growth,  until  destroyed  by 
cultivation.1 

The  flow  of  irrigation  water  produces  the  same  compacting 
effect,  but  to  a  less  extent;  the  more  as,  unlike  rain  water,  irri- 
gation water  usually  contains  a  certain  amount  of  alkaline  and 
earth  salts,  which  tend  to  prevent  the  diffusion  of  clay  and  of 
fine  sediments,  and  therefore  the  disintegration  of  the  soil-floc- 
cules  into  single  grains.  Nevertheless,  it  is  in  some  soils  as 
necessary  to  cultivate  after  surface-irrigation  as  after  rains, 
in  order  to  prevent  great  waste  of  moisture  by  evaporation. 

Determination  of  rate  of  percolation. — When  water  is  al- 


1  This  effect  is  well  illustrated  by  the  behavior  of  a  dry  brick  laid  upon  a  wet 
sponge.  It  will  quickly  absorb  all  the  liquid  moisture  contained  in  the  latter, 
while  the  sponge  will  be  wholly  unable  to  take  any  moisture  from  a  fully-soaked 
brick. 


222  SOILS. 

lowed  to  soak  into  an  air-dry  soil  column  without  sensible  shock 
or  motion,  from  a  constant  level,  we  obtain  the  nearest  ap- 
proach to  a  definite  determination  of  the  relative  permeability 
of  soils  to  water  under  the  conditions  usual  in  the  arid  region. 
A  number  of  determinations  thus  made  is  tabulated  in  the  dia- 
gram given  below,  which  embodies  the  observations  made  by 
Mr.  A.  V.  Stubenrauch  1  in  connection  with  a  more  extended 
investigation. 

As  these  experiments  were  made  with  soils  not  in  their  field  con- 
dition, but  gently  broken  up  with  a  rubber  pestle,  a  standard  of  com- 
pactness was  established  by  weighing  the  quantity  which  could  con- 
veniently be  settled  into  a  tube  space  of  100  centimeters  capacity  by 
tapping  the  sides  and  bottom  of  the  tube,  without  touching  the  soil 
itself.  In  this  way  the  following  standards  were  established  :  For  the 
University  Adobe  soil,  140  grams  ;  for  the  Yuba  loam  soil,  no  grams  ; 
for  the  Stanislaus  sandy  soil,  170  grams.  Tubes  i^  inches  wide  were 
used,  and  the  soils  were  introduced  in  bulk,  inside  of  a  cylinder  of  stiff 
paper  upon  which  previously  to  rolling  it  up  the  soils  had  been  thoroughly 
mixed.  After  introducing  the  soil-filled  paper  roll  it  was  gently  with- 
drawn, leaving  the  soil  column  in  the  tube  as  uniform  as  before  ;  a  con- 
dition almost  impossible  of  fulfilment  when  the  soil  is  introduced  piece- 
meal. The  tubes  were,  of  course,  left  open  at  the  lower  end,  using  a 
wire  netting  to  keep  the  soil  column  in,  so  that  the  air  could  escape 
freely  before  the  descending  water  column. 

The  results  thus  obtained  do  not,  of  course,  apply  directly  to  the 
same  soils  undisturbed  in  place  in  the  field ;  where,  moreover,  the  air  is 
confined  by  the  wetting  of  the  surface  and  thus  directly  opposes  pen- 
etration of  the  water.  Still,  they  doubtless  give  a  correct  idea  of  their 
relative  permeability  for  water  when  in  the  tilled  condition.  The  water 
level  was  automatically  maintained  at  the  depth  of  half  an  inch  above 
the  surface  of  the  soil  columns.  Pore-spaces  given  are  calculated  from 
volume-weight  and  specific  gravity. 

This  diagram  shows  plainly  that  there  is  no  direct  relation 
between  the  total  pore-space  in  a  soil  and  the  facility  of  water- 
penetration.  The  highest  pore-space,  in  the  fine-grained  allu- 
vial loam,  allows  more  rapid  percolation  than  the  heavy  clay  or 
adobe  soil,  but  is  greatly  exceeded  by  the  coarser  sandy  soil. 
In  all  it  is  very  apparent  that  the  downward  movement  slows 
down  as  the  water  descends,  doubtless  because  the  great  fric- 
tion in  a  longer  column  gradually  diminishes  the  effect  of  hy- 

1  Rep't  Calif.  Exp't  Station  for  1898  to  1901,  p.  165. 


THE  WATER  OF  SOILS. 


223 


Blac 
4 

For 

ex. 

c 

*=» 

Surface 
Ins. 

2 
4 
6 
8 
10 
12 
14 
16 
18 
20 
22 
24 
26 
28 
30 
32 
34 
36 
38 

40 
t,-.- 

kAdo 

2.83% 

espa 

be, 

ce                     PC 
f    <3             ^ 

b     •*-•                       o_ 

^    ^j              Q} 
Surface 
Ins: 

0    24-                  2 

1        31      r>^          "4 

Loam, 
57.36% 

respa 

San 
3 
ce                   Po 

0        C                               "" 

Ins. 

0     24                   2 

dy  So 
7.10% 

respa 

11, 

ce 

"^      _^> 

Ij 

0     15 
1      0 

2    a 

5    43 
8    13 
II     7 
13    55 

n    7 

20  55 
25  .31 
30  55 
36    55 
42  55 
48  55 
55 
61    19 
61    31 
73  55 
80   49 

rent  soils. 

•'.•:.<.."•••:' 

::  S| 

">•-.; 

:/£4 

&£/£ 

i      39                   4 

*?.•"-•'"•' 

•^  •'.•/:'-'i 

,'•  -'  /•  '-, 

an             e 

5     48     6  Hr&.  8 

fc-SS 

3      16             ""  "T6- 
5     48                  8 
8    48          """-10. 
42    24                 12 
IS      0         **  ^  14 
19   48                  i& 
23    54                  18 
28    13  X  ^       20 
33     6                  22 
38*  ^8>  $6          24 
44    42.                  26* 
5pt3^  ^        28 

.v-V  '•.*,•. 

p; 

9    12.                 10 

IT    24                  <4 
21    30                  16 
26    \Z~~~"~^\Q~ 
32      5                   20 

43    54                   24 

:iSj 

'-"if  ^  ;'"• 

til 

f'-'l&i 

^ii'l 

^••^v 

^•n-?1.; 

V^ 

?;V;$ 

•'*»:'  '•*./' 

n 

^,   ''  i-    i  '  i 

",  '    V-  •*"- 

'*£'<£'• 

"'•fcs 

:f  '•**•.'• 

v-v:!-';.' 

•'"•'  ••':;' 

'rr-r* 

'•*  '.''."•• 

i  .  V* 

'•'.:"•"-;  :, 

^s 

.1    .  V,' 

55    35                   28 
81    53                    34 

^ 

;.;  ':'-•'• 

;:>:r- 

58    36                  30 

"^    6                    34 
80    12      Nl\      36 

N 

83    18                 33 
36    18                  40 

:'»  "•  "•"  •' 

:;-  '  ;'•' 

-'-•;,;  L 

.,'~'-.'.V- 

T_  -  ,  *  *  - 

82          ~~  --^J    36 

'     "v''?. 

101    30                    38 

"~f'-~t 

^•^r; 

'"  •  *  :  • 

H3   47.                   40 

-''•'•«  '•' 

•£«£•? 

CT),    Hifff 

224 


SOILS. 


drostatic  pressure.  It  may  be  presumed  that  at  a  certain  dis« 
tance  from  the  surface  the  downward  movement  becomes  prac- 
tically uniform,  and  independent  of  the  pressure  from  above. 
Summary. — Two  salient  points  are  revealed  by  even  a  cur- 
sory inspection  of  the  preceding  diagram,  viz. : 

1.  The  downward  percolation  is  most  rapid  in  the  same 
soils  in  which  the  capillary  ascent  is  quickest,  that  is,  in  the 
coarse,  sandy  soil. 

2.  The  rapidity  of  percolation  decreases  materially  as  the 
wetted  soil  column  increases  in  length. 

The  first  point  is  readily  foreseen  and  needs  no  comment.  As  re- 
gards the  second,  it  results  from  the  fact  that  as  the  wetted  column 
lengthens  the  frictional  resistance  increasingly  counteracts  the  effects 
of  the  hydrostatic  pressure  from  above,  until  the  water's  descent  becomes 
but  little  more  rapid  than  would  be  its  lateral  diffusion,  or  its  ascent  at 
the  end  of  a  similar  column  supplied  by  capillary  rise  from  below.  In 
both  cases  the  frictional  resistance  has  so  far  counteracted  the  effect  of 
gravity  that  the  capillary  coefficients  of  the  soil-material  become  the 
controlling  factors  of  the  water  movement. 

Influence  of  Variety  of  Grain-sizes. — King  (Physics  of 
Agriculture,  pp.  159  ,160),  compared  the  rapidity  of  the  per- 
colation of  water  through  definitely  graded  pure  sands  on  the 
one  hand,  and  a  sandy  loam  and  a  clay  soil  on  the  other.  The 
materials  were  arranged  in  8-foot  columns  fully  saturated  with 
water  at  the  outset,  and  then  allowed  to  drain  freely.  The 
following  abridged  table  shows  the  tenor  of  his  results : 

TABLE   SHOWING    RELATIVE    RAPIDITY  OF   PERCOLATION   IN   PURE   SANDS 
AND   SOILS,   IN   INCHES   OF   WATER   DRAINED   OFF. 


Diameter  of   Uniform    Sand 
Grains. 

First 
30  minutes 

Second 
30  minutes. 

Total 
in  one  hour. 

.475  mm. 

•us    " 
.083    " 

10.25 
5.67 

1.  21 

4.68 

4.52 

.85 

'4-93 
10.19 
2.06 

Soils. 

First  21- 
23  hours. 

First  10 
days 
following. 

Second  10 
days 
following. 

Total  in 
about 
505  hours. 

Sand} 
Clay 

2.64 
1.96 

5-07 

2.  II 

.91 

•49 

8.62 
4-5° 

loam  

THE  WATER  OF  SOILS.  22$ 

This  table  is  very  instructive  in  showing  the  great  difference 
in  the  rapidity  of  percolation  in  materials  of  uniform,  even- 
sized  grains,  as  compared  with  such  as  contain  particles  of 
many  different  sizes,  in  which  the  interspaces  of  the  larger  ones 
are  filled  more  or  less  closely  by  the  smaller  sizes  of  particles 
(see  chapter  7,  p.  109).  While  it  is  true  that  we  have  no  defi- 
nite physical  analysis  of  the  soils  here  used,  the  differences  are 
so  great  as  to  be  sufficiently  striking.  Compare  the  percolation 
through  the  sand  of  .155  mm.  uniform  grain-size  (a  fine 
sand),  during  the  first  half  hour,  with  that  through  the  sandy 
loam  during  the  first  21  hours.  Twice  as  much  water  has 
passed  from  the  sand  as  from  the  soil  in  one  forty-second  part 
of  the  time.  Comparing  similarly  the  finest  sand,  .083  mm.  in 
diameter,  with  the  clay  loam,  we  find  the  difference  to  be  as 
one  to  seventy-three.  It  is  thus  evident  that  but  for  the  vari- 
ously assorted  sizes  of  the  soil-particles,  water  \vould  not  be 
held  long  enough  to  supply  plant  growth. 

Percolation  in  Natural  Soils. — In  artificial  percolation  ex- 
periments, as  well  as  during  a  fall  of  rain,  the  gradual  settling 
of  the  fully  wetted  soil-column  produces  a  compacting  of  that 
portion  of  the  mass,  that  increasingly  impedes  the  downward 
penetration.  The  effect  of  this  under  natural  conditions  is 
readily  seen  in  the  fact  that  after  the  first,  rapid  absorption  of 
falling  rain  by  the  soil  when  in  good  tilth,  there  is  a  gradual 
slackening  of  the  process  even  when  the  rain  is  fine  and  slow, 
causing  a  perceptible  increase  of  the  runoff  until,  should  the 
rain  continue  for  some  time,  the  absorption  becomes  so  slow 
as  to  cause  all,  or  nearly  all  the  water  to  drain  off  the  surface. 
The  soil  is  then  called  "  saturated,"  having  really  arrived  at 
that  point  right  at  the  surface,  and  to  a  depth  varying  accord- 
ing to  the  duration  and  amount  of  rain,  and  the  natural  per- 
viousness  of  the  land. 

When  the  rain  ceases,  the  visible  saturation  of  the  surface 
usually  soon  disappears  in  cultivated  soils,  and  the  zone  of 
saturation  begins  to  descend.  The  progress  of  this  descent 
may  be  very  strikingly  observed  in  a  series  of  holes  (post- 
holes)  dug  or  bored  across  a  ridge;  as  indicated  in  the  sub- 
joined schematic  diagram,  in  which  the  successive  dotted  lines 
represent  the  levels  of  the  descending  "  bottom  water  "  at  suc- 

15 


226  SOILS. 

cessive  intervals,  as  derived  from  the  observation  of  the  water 
levels  in  the  several  holes.1 


FIG.  42. — Percolation  in  clay  land  after  heavyrain. 

It  will  be  seen  that  while  at  first  the  upper  surface  of  the  zone  of 
saturation  coincides  with  the  surface  of  the  ground,  in  falling  it 
descends  most  rapidly  on  the  highest  ground,  while  at  the  lower  levels 
the  holes  may  remain  full  or  overflowing ;  the  drainage  taking  place 
sideways  as  well  as  vertically.  The  curved  surface  connecting  the  levels 
in  the  several  holes  gradually  flattens,  rapidly  at  first,  then  progressively 
more  slowly ;  the  water  disappearing  entirely,  first  from  the  holes  lying 
highest,  then  successively  from  those  at  lower  levels ;  those  located  in 
valleys  or  drainage  channels  remaining  full  until  surface-water  ceases  to 
run  in  such  channels.  But  even  after  liquid  water  has  ceased  to  be 
visible  in  the  holes,  the  descent  of  the  water  continues  within  that  por- 
tion of  the  soil,  tending  (unless  more  rain  should  come  before  that  time), 
to  establish  the  condition  of  equilibrium  as  existing  in  the  soil  columns 
shown  in  the  diagram  on  p.  205,  chapt.i  i  ;  such  as  results  from  the  capil- 
lary ascent  of  water  from  below,  but  having  above  it  a  column  of  soil 
of  minimum  water-content,  of  greater  or  less  height  according  to  the 
length  of  time  allowed  for  the  water  to  descend.  This  is  a  very  common 
state  of  things  during  the  long  summer  droughts  in  the  arid  region, 
when  neither  rain  nor  irrigation  has  added  to  the  water  supply  in  the 
soil  for  many  months,  and  yet  ordinary  deciduous  fruit  trees  mature 
their  normal  crops.  Frequently,  however,  before  this  state  of  equilibrium 
is  reached,  evaporation  from  the  surface  so  draws  upon  the  water  supply 
within  the  first  few  feet,  as  to  reduce  the  soil  to  undersaturation  at  the 
lowest  point  of  the  descending  column,  so  stopping  farther  descent  and 
soon  reversing  the  direction  of  the  movement.  The  latter  is  the  usual 
condition  of  scantily  irrigated  ground. 

1  The  exact  record  of  these  observations  was  unfortunately  destroyed  by  fire 
the  soil  was  a  heavy  clay,  and  it  took  ten  days  before  the  water  disappeared  from 
the  lowest  hole. 


THE  WATER  OF  SOILS.  227 

Ground  or  Bottom  Water,  Water  Table. — During  and  after 
long-continued  and  abundant  rains,  the  zone  of  supersatura- 
tion  continues  to  descend  until  it  finally  reaches  a  more  or  less 
permanent  level,  varying  somewhat  from  season  to  season,  but 
on  the  whole  usually  definable  for  each  region  and  locality; 
being  the  depth  to  which  wells  must  be  sunk  in  order  to  secure 
a  fairly  permanent  water  supply.  This  is  called  the  water 
table,  ground  water,  bottom  water,  or  "  first  water."  1  The 
proportion  of  the  rainfall  that  reaches  the  permanent  water 
level  varies  enormously,  of  course,  in  different  soils  and  at 
different  times.  With  brief  and  moderate  rains,  in  soils  of 
high  water-holding  power  and  slow  percolation,  it  may  never 
reach  the  bottom-water  level;  this  is  very  commonly  the  case 
in  the  arid  regions.  Where,  as  in  the  humid  regions,  rains  are 
frequent  or  much  prolonged,  one  half  and  even  more  may 
finally  reach  the  permanent  level ;  runoff  and  evaporation  dis- 
posing of  the  balance. 

Lysimeters. — For  the  determination  of  the  amount  of  water  percolat- 
ing to  given  depths,  water-tight  receptacles  called  lysimeters  are  usually 
employed.  The  best  way  to  establish  such  receptacles  is  to  isolate  a 
unit-area  (usually  a  square  meter)  by  digging  all  around  it  to  the  depth 
desired,  then  surrounding  it  with  a  metal  sheet  soldered  tightly  at  the 
cut  edges,  and  finally  driving  in  a  sharp-edged,  stiff  metal  sheet  so  as 
to  form  the  bottom  when  soldered  to  the  upright  walls ;  leaving  on  one 
side  an  outlet  for  the  percolating  water,  which  is  then  received  into  a 
measuring  receptacle  somewhat  like  a  rain  gauge. 

Hall  (The  Soil,  p.  75)  states  that  at  Rothamstead,  where  an 
average  rainfall  of  31.3  inches  is  distributed  rather  uniformly 
through  the  season,  and  where  the  soil  is  a  moderately  clayey 
loam,  a  little  less  than  half  percolates  through  20  inches  of 
soil,  and  about  4$c/<  through  60  inches. 

Surface  of  Ground  ll'atcr;  Variations. — The  surface  of  the 

1  In  contradistinction  to  other  levels  or  "streams  "  of  water  which  may  usually 
be  found  lower  down,  separated  from  the  first  water  by  some  impervious  stratum 
of  clay,  hardpan  or  rock,  and  very  commonly  under  sufficient  pressure  to  rise 
somewhat  higher  than  the  point  at  which  it  was  struck,  owing  to  connection  with 
higher-lying  sources  of  supply.  When  such  pressure  is  sufficient  to  cause  an 
overflow  at  the  surface  of  the  ground,  we  have  "  Artesian  "  water  as  commonly 
understood. 


228  SOILS. 

water  table,  however,  is  rarely  level  except  in  level  and  very 
uniform  ground,  or  after  long  periods  of  drought.  The  un- 
dulations of  its  surface  conform,  in  general,  to  that  of  the 
ground  surface,  but  are  less  abrupt;  so  that  the  water  lies 
nearer  to  the  surface  in  low  than  in  high  ground,  as  is  indi- 
cated in  the  diagram  above. 

King  *  has  shown,  moreover,  that  the  level  of  the  ground 
water  shows  sensible  variations  due  to  increased  or  diminished 
barometric  pressure,  as  well  as  to  variations  of  temperature  in 
the  soil,  which  cause  the  air  in  the  pores  to  expand  or  contract 
to  a  degree  sufficient  to  bring  about  variations  in  the  flow  of 
springs  and  underdrains  to  the  extent  of  8  and  15%  respect- 
ively, in  conformity  with  the  daily  changes  of  temperature 
and  pressure. 

The  Depth  of  the  Ground  Water  most  Favorable  to  Crops 
cannot  be  stated  in  a  general  manner,  as  it  depends  materially 
upon  the  nature  of  the  crop,  its  root  habit,  and  the  nature  of  the 
soil.  As  has  already  been  said,  the  amount  of  soil-moisture 
most  favorable  to  plant  growth  is  about  half  of  the  maximum  it 
can  hold ;  and  this  condition,  as  is  shown  in  the  table  in  chapter 
n,  p.  208,  is  reached  about  the  middle  of  the  maximum  height 
to  which  the  water  can  rise  by  capillarity  from  the  water  level. 
Below  this  point  the  access  of  air  to  the  roots  becomes  too 
limited,  and  in  case  of  continuous  rains  the  root-ends  would 
soon  begin  to  suffer  from  want  of  aeration.  On  "  sub-irri- 
gated "  land,  therefore,  which  is  generally  considered  desirable, 
crops  must  be  carefully  selected  with  respect  to  their  root 
habits.  Thus  while  alfalfa  needs  considerable  moisture  to  do 
its  best,  its  deep-rooting  habit  renders  it  undesirable  when  the 
ground  water  is  at  less  than  five  feet  depth ;  but  red  clover  may 
be  grown  even  with  the  water  level  at  three  feet. 

In  clayey  soils  root-penetration  is  always  less  than  in  sandy 
lands;  and  although  in  the  former  the  capillary  ascent  of  water 
goes  higher  than  in  the  latter,  yet  its  movement  in  clays  is  so 
much  slower  than  in  sandy  materials  that  unless  water  is  within 
comparatively  easy  reach,  the  plants  may  suffer  from  drought. 
Experience  has  long  ago  fixed  the  proper  depth  at  which  to 
lay  underdrains  limiting  the  rise  of  bottom  water,  at  from 
three  to  four  and  a  half  or  even  five  feet  in  clay  soils;  greater 

1    Physics  of  Agriculture,  p.  270. 


THE  WATER  OF  SOILS. 


229 


depths  are  only  exceptionally  used,  partly  because  the  laying 
of  drains  then  becomes  too  expensive. 

A  mass  of  four  feet  of  clay-loam  soil  is  commonly,  then,  con- 
sidered as  sufficient  to  supply  the  needs  of  a  crop ;  it  being 
understood  that  in  the  humid  region  at  least,  such  soils  are 
usually  the  richest  in  plant  food,  so  that  a  deeper  range  of  the 
root  system  is  not  called  for.  It  is  quite  otherwise  in  the  sandy 
soils  of  the  same  region,  which  being  usually  poor  in  plant 
food,  must  afford  a  deeper  penetration  in  order  that  an  ade- 
quate amount  of  the  same  shall  be  within  reach  of  the  roots. 
Sandy  lands,  then,  should  be  deep  in  order  to  repay  cultivation ; 
and  fortunately  this  is  usually  the  case.  But  when  this  is 
otherwise ;  when  for  instance  a  sandy  soil  four  feet  in  depth  is 
underlaid  by  impervious  clay,  underdrains  may  be  quite  as  nec- 
essary as  in  the  clay  lands;  since  the  depth  of  actually  available 
soil  mass  would  otherwise  be  reduced  to  two  or  two  and  a  half 
feet  only,  by  the  water  stagnating  on  the  clay  surface  and  rising 
from  1 6  to  24  inches  in  the  sand.  Soils  thus  shallowed  can 
with  difficulty  be  maintained  in  good  productive  condition  even 
by  the  most  energetic  fertilization. 

Moisture  supplied  by  tap  roots. — In  most  cases,  sandy  lands 
do  not  require  underdraining;  and  in  them,  root-penetration 
may  reach  to  extraordinary  depths  in  the  case  of  certain  plants, 
especially  when  tap-rooted.  Thus  the  roots  of  alfalfa  (lucern) 
are  very  commonly  found  to  reach  depths  of  twenty  to  twenty- 
five  feet,  and  even  sixty  feet  has  been  credibly  reported  for  the 
same  plant  in  the  arid  region.  It  is  obvious  that  for  such 
plants,  a  high  level  of  l>ottom  water  is  wholly  undesirable,  since 
they  are  enabled  to  obtain  their  moisture  supply  from  great 
depths,  and  can  thus  utilize  for  their  nutrition  much  larger  soil- 
masses  than  can  shallow-rooted  plants. 

Reserve  of  Capillary  ll'atcr. — It  must  be  remembered  that  it 
is  not  only,  nor  usually,  the  bottom  water  that  supplies  moisture 
to  plant  growth;  for  all  soils  of  proper  texture  for  cultivation 
retain  within  them  a  certain  amount  of  capillary  moisture  after 
the  ground  water  has  reached  its  permanent  level  (  see  this 
chap.  p.  226),  and  when  the  tap  or  main  roots  are  plentifully 
supplied  with  water,  the  upper  and  chief  feeding  roots  draw 
but  lightly  upon  the  moisture  within  their  immediate  reach  for 
the  purpose  of  leaf  evaporation.  This  fact  can  be  plainly  ob- 


230 


SOILS. 


served  in  the  arid  region,  when  on  the  advent  of  the  summer 
drought,  young  plantlets  whose  tap  roots  have  reached  a  cer- 
tain depth  continue  to  flourish  and  develop,  while  others  prac- 
tically of  the  same  age,  but  slightly  behind,  quickly  succumb, 
though  the  feeding  roots  of  both  may  draw  upon  the  same  soil 
layer.  It  is  especially  in  sandy  soils  that  moisture  is  naturally 
thus  conserved  in  the  upper  layers,  because  of  the  failure  of  the 
water  to  rise  by  capillary  ascent  so  as  to  evaporate  from  the 
surface  layer.  It  is  often  surprising  to  find  a  good  amount  of 
moisture  in  the  sandy  soils  of  desert  regions  at  the  depth  of 
eight  of  eight  or  ten  inches,  when  the  surface  is  so  hot  as  to 
scorch  the  fingers;  and  this  moisture  continues  very  uniformly 
to  great  depths,  probably  to  bottom  water  lying  twenty  or 
more  feet  below  the  surface,  which  in  such  materials  may 
readily  by  reached  by  tap-rooted  plants  such  as  the  "  sage- 
brush "  (Artemisia  tridentata),  the  saltbushes  (Atriplex)  and 
others. 

Injurious  Rise  of  Bottom  Water  resulting  from  Irrigation. 
— In  the  deep,  pervious  sandy  lands  of  the  arid  region,  especi- 
ally where  the  rainfall  is  very  low  and  can  wet  the  soil  annually 
only  to  two  or  three  feet  depth,  the  substrata  are  sometimes 
found  to  be  barely  moist  to  depths  of  thirty  and  forty  feet, 
and  the  short-lived  spring  vegetation  carries  off  during  its 
growth  all  the  moisture  supplied  by  the  winter  rains.  When 
such  lands  are  subjected  to  irrigation  and  the  ditches  carrying 
the  water  are  simply  dug  into  the  natural  sandy  land,  the  thirsty 
soil  absorbs  the  water  greedily,  so  that  even  a  considerable 
volume  of  water  makes  but  slow  progress  toward  the  farther 
end  of  the  canals.  Gradually,  as  the  rapidity  of  absorption 
decreases,  the  diminution  of  flow  becomes  less  sensible,  but 
still  the  loss  thus  experienced  may  be  a  very  considerable  per- 
centage of  the  whole  supply.  Thus  in  the  Great  Valley  of 
California,  as  well  as  in  portions  of  Wyoming  (Bull,  61,  p. 
32),  the  permanent  loss  from  seepage  is  in  the  case  of  some 
extensive  irrigation  systems  estimated  at  fully  50  per  cent. 
When  such  lands  have  a  considerable  slope,  the  injury  com- 
monly ends  with  the  loss  of  the  water,  which  in  many  cases  is 
again  gathered  and  utilized  at  a  lower  level.  But  when  the 
lands  have  but  a  slight  slope,  the  drainage  may  become  so  slow 
as  to  permit  of  the  gradual  rise  of  the  seepage  water  in  the 


THE  WATER  OF  SOILS.  23! 

substrata,  until  finally  it  may  come  to  within  a  few  feet  of,  or 
actually  to  the  surface. 

Consequences  of  the  Swamping  of  Irrigated  Lands. — The 
injurious  consequences  of  this  swamping  of  the  irrigated  lands 
may  readily  be  imagined.  The  first  effect  is  usually  noted  in 
the  sickening  or  dying-out  of  orchards  and  vineyards,  conse- 
quent upon  the  submergence  of  the  deeper  roots,  which  in 
such  lands  frequently  reach  to  from  fifteen  to  twenty  feet  be- 
low the  surface.  But  even  where  pre-existing  plantations  are 
not  in  question,  the  shallowing  of  the  soil-  and  subsoil-strata 
from  which  the  plants  may  draw  their  nourishment,  consti- 
tutes a  most  serious  injury  to  the  cultural  value  of  the  land. 
It  has  become  unsuitecl  to  deep-rooted  crops ;  and  where  the 
natural  soil,  alone,  would  have  perpetuated  fertility  for  many 
years,  fertilization  becomes  necessary  within  a  short  time. 
The  injury  becomes  doubly  great  when,  as  is  frequently  the 
case,  the  rising  bottom  water  brings  up  with  it  to  the  surface 
soil  the  alkali  salts  which  previously  were  distributed  through- 
out many  feet  of  substrata,  frequently  rendering  profitable 
cultivation  impossible  where  formerly  the  most  luxuriant  crops 
were  grown. 

Theoretically  of  course  it  is  perfectly  easy  to  avoid  or  rem- 
edy these  troubles.  It  is  only  necessary  to  render  the  ditches 
water-tight  by  puddling  with  clay,  cement,  or  otherwise.  But 
the  heavy  cost  of  this  improvement  forms  a  serious  obstacle 
to  its  adoption  by  the  ditch  companies  who  are  not  themselves 
owners  of  land.  Thus,  extensive  areas  of  lands  which  when 
first  irrigated  were  among  the  most  productive,  have  in  the 
course  of  eight  or  ten  years  become  almost  valueless  to  their 
owners,  to  whom  legislation  thus  far  affords  but  distant  prom- 
ise of  relief;  although  the  case  seems  in  equity  to  fall  clearly 
within  the  limits  of  the  laws  governing  trespass. 

Permanent  Injury  to  Certain  Lauds. — In  cases  like  those  al- 
luded to  the  remedy  usually  available  for  higher  ground-water 
does  not  always  afford  relief,  even  when  otherwise  available. 
Long-continued  submergence  produces  in  many  soils  effects 
which  cannot  easily,  if  at  all.  be  overcome  by  subsequent  aera- 
tion. This  is  most  emphatically  true  of  soils  containing  a 
large  proportion  of  ferric  hydrate  in  the  finely  divided  form 
in  which  it  is  usually  present  in  "  red  "  soils. 


232  SOILS. 

The  first  effect  of  the  stagnation  of  water  in  such  lands  (as 
already  explained  in  a  former  chapter  (3,  p.  45)  is  to  set  up  a 
reductive  (bacterial)  fermentation  of  the  organic  matter  of 
the  soil,  transforming  the  ferric  into  ferrous  hydrate,  which 
in  the  presence  of  the  carbonic  acid  simultaneously  formed,  be- 
comes ferrous  carbonate,  readily  soluble  in  carbonated  water. 
That  this  compound  is  poisonous  to  plant  growth,  has  been 
stated  (chap.  3,  p.  46).  The  carbonates  of  lime  and  magnesia 
are  simultaneously  dissolved  by  the  same,  as  is  also  calcic  phos- 
phate, the  usual  form  in  which  phosphoric  acid  is  present  in 
the  soil.  Under  the  influence  of  partial  aeration  from  the 
surface,  the  ferrous  carbonate  is  slowly  re-transformed  into 
ferric  hydrate,  aggregated  in  the  form  of  spots  or  concretions 
of  "bog  ore"  (see  chapter  5,  p.  66).  In  this  process  the 
greater  part  of  the  phosphoric  acid  of  the  soil  is  also  abstracted 
from  its  general  mass  and  concentrated  in  the  bog  ore  (chap.  5, 
p.  65),  in  which  it  is  wholly  unavailable  to  vegetation,  and 
cannot  be  made  available  while  in  the  ground,  by  any  known 
process.  The  soil  is  therefore  permanently  impoverished  in 
phosphoric  acid ;  it  is  also  deprived  of  its  content  of  ferric  hy- 
drate, and  is  transferred  from  the  class  of  "  red  "  to  that  of 
"  white  "  soils,  well  known  everywhere  to  be  unthrifty  and  to 
require  early  fertilization.  Not  only  is  this  true,  because  of 
their  almost  invariable  poverty  in  phosphoric  acid,  but  also 
usually  in  lime,  which  like  the  iron,  if  not  leached  out,  is  aggre- 
gated into  concretions  in  the  subsoil,  leaving  the  surface  soil 
depleted  of  this  important  ingredient.  The  humus,  also,  is 
either  destroyed  or  at  least  "  soured  "  at  the  same  time. 

Reduction  of  Sulfates. — Should  such  a  soil  contain  any  considerable 
amount  of  sulfates,  especially  in  the  form  of  gypsum  or  calcic  (or 
magnesic)  sulfate,  the  reductive  process  results  in  the  formation  of 
iron  pyrites  (ferric  sulfid,  chap.  5,  p.  75)  ;  while  at  the  same  time  the 
soil  is  often  sufficiently  impregnated  with  sulfuretted  hydrogen  as  to 
be  readily  perceived  by  the  odor,  or  by  the  blackening  of  a  silver  coin. 
This  is  very  commonly  the  case  in  seacoast  marshes,  where  a  hole  made 
with  a  stick  thrust  into  the  mud  will  be  found  to  give  forth  both  car- 
buretted  and  sulfuretted  hydrogen,  while  a  careful  washing  of  the  soil 
will  reveal  the  presence  of  minute  crystals  of  iron  pyrites.  Hence  the 
need  of  prolonged  aeration  of  marsh  soils,  effecting  the  peroxidation  of 


THE  WATER  OF  SOILS.  233 

the  ferrous  compounds,  and  the  conversion  of  the  pyrites  first  into 
ferrous  sulfate,  and  subsequently  into  innocuous,  yellow,  insoluble 
ferric  oxy-sulfate. 

Ferruginous  Lands. — The  injurious  effect  of  the  swamping 
of  ferruginous  lands  has  been  especially  conspicuous  in  some 
of  the  irrigated  rolling  lands  of  the  Sierra  Foothills  of  Cali- 
fornia, where  orchards  planted  in  relatively  low  ground  and 
in  full  bearing  have  succumbed  to  the  poisonous  effects  of  the 
ferrous  carbonate  formed  in  the  subsoil,  long  before  the  water 
had  risen  so  high  that,  had  the  trees  been  grown  afterwards, 
they  would  have  adapted  their  root  system  to  the  existing  con- 
ditions and  fared  moderately  well  at  least.  Underdrainage  of 
the  lower  lands  is,  of  course,  the  only  possible  remedy  for  this 
state  of  things,  although  even  then  the  root-penetration  is  much 
more  restricted,  and  therefore  natural  fertility  of  much 
shorter  duration,  than  would  have  been  the  case  without  the 
rise  of  the  irrigation  water. 

It  is  thus  clear  that  in  the  practice  of  irrigation,  the  liability 
of  injury  to  the  lower  ground  by  "  swamping  "  through  the 
rise  of  the  ground  water  should  always  be  kept  in  view;  that, 
in  fact,  irrigation  and  provision  for  drainage  should  always  go 
hand  in  hand.  The  legal  provisions  facilitating  the  rights-of- 
way  for  irrigation  ditches  should  be  made  equally  cogent  with 
respect  to  drainage. 


CHAPTER  XIII. 

WATER  OF  SOILS  (Continued). 

THE   REGULATION   AND    CONSERVATION   OF  SOIL  MOISTURE. 

IN  view  of  the  commanding  importance  of  an  adequate 
supply  of  water  to  vegetation,  the  possible  and  available  means 
of  assuring  such  supply  by  utilizing  to  the  best  advantage  both 
rainfall  and  irrigation  water,  require  the  closest  consideration. 

Loosening  of  the  Surface. — The  first  thing  needful,  of 
course,  is  to  allow  the  water  free  opportunity  to  soak  into  the 
soil,  so  as  to  moisten  the  land  as  deeply  as  possible.  That  to 
this  end  the  surface  should  be  kept  loose  and  pervious  by  till- 
age, breaking  up  crusts  that  may  have  been  formed  by  the  beat- 
ing of  rains,  has  already  been  discussed.  In  the  case  of  heavy 
clay  soils,  however,  this  alone  is  not  always  sufficient.  The 
most  effectual  way  to  loosen  the  land  to  greater  depths  than 
can  be  reached  by  tillage,  is  by  means  of  underdrains  laid  at 
the  greatest  depth  that  is  practically  admissible. 

Effects  of  Underdrains. — That  drain  tiles  laid  for  the  ex- 
press purpose  of  carrying  off  surplus  water  should  help  to  con- 
serve soil  moisture,  seems  at  first  sight  to  be  a  paradox.  Yet 
the  explanation  of  the  fact,  which  has  been  demonstrated  by 
long  experience,  is  not  difficult.  The  effect  is  most  striking  in 
clay  soils,  for  sandy  soils  are  commonly  naturally  underdrained 
already. 

In  discussing  the  changes  of  volume  which  soils  undergo  in 
wetting  and  drying,  the  fundamental  points  in  the  premises 
have  already  been  mentioned  (see  chap.  7,  p.  112).  Clay  soils 
in  drying  shrink  considerably,  and  re-expand  on  wetting,  but 
rather  slowly :  moreover,  some  clays  crumble  when  wetted 
after  drying,  while  others,  very  plastic  when  wet,  crumble  on 
drying  (see  chap.  /,  p.  116). 

It  follows  that  while  a  clay  subsoil  when  kept  permanently 
wet,  will  form  a  uniform,  p?.sty,  difficultly  penetrable  mass: 

234 


THE  WATER  OF  SOILS. 


235 


when  subjected  to  frequent  alternate  wetting  and  drying,  it 
becomes  fissured  and  crumbly,  so  as  to  resemble  in  its  texture 
a  tilled  soil.  This  frequent  alternation  of  wetting  and  drying 
is  precisely  what,  in  the  course  of  time,  is  brought  about  by 
unclerdrains;  rendering  clay  subsoils  pervious  both  to  air  and 
water.  The  consequence  is  that  even  heavy  rains  can  be  fully 
absorbed  by  the  soil  mass  lying  above  the  drains,  the  surplus 
draining  off  readily  in  a  short  time.  Roots  therefore  can  not 
only  penetrate,  but  exercise  their  vegetative  functions  perfectly 
at  the  full  depth  of  the  drains.  They  are  still  at  liberty  to  pene- 
trate as  much  deeper  as  their  demands  for  moisture  may  re- 
quire; but  the  depth  of  four  to  four  and  a  half  feet  is  already 
so  much  greater  than  in  the  humid  region  would  usually  be 
reached  by  them  in  undrained  clay  soils,  that  commonly  the 
moisture  successively  retained  within  that  mass  is  as  much  as  is 
required  by  them  during  the  growing  season.  At  the  same 
time,  their  feeding  roots  are  so  far  below  the  surface,  that 
ordinary  short  droughts  do  not  reach  them  at  all ;  while  the 
underdrains  prevent  any  injurious  stagnation  of  water  around 
them.  It  need  hardly  be  added  that  the  entire  task  of  cultiva- 
tion is  also  greatly  facilitated;  not  only  because  drained  soils 
can  be  plowed  within  a  few  hours  after  the  cessation  of  rains, 
as  against  the  same  number  of  days  that  would  have  to  elapse 
in  the  undrained  areas;  but  because  tillage  is  easier,  and  less 
draft  is  required,  even  when  it  is  carried  to  a  much  greater 
depth. 

Underdrainage,  then,  must  be  counted  as  being  among  the 
most  effective  means  both  of  utilizing  the  rainfall  so  as  to  pre- 
vent loss  from  runoff  and  injury  from  washing,  and  of  creat- 
ing a  deep,  loose,  pervious  soil  mass,  well  adapted  to  root  pene- 
tration as  well  as  to  the  conservation  of  moisture;  rendering 
possible  timely  tillage  and  cultivation,  and  early  development 
of  crops  fully  supplied  with  moisture  and  therefore  secure 
against  loss  from  drought.  The  safety  and  improvement  of 
crops  thus  secured  corresponds  in  the  humid  region  to  that 
brought  about  by  the  command  of  irrigation  water  in  the  arid 
countries.  But  it  by  no  means  follows  that  underdrainage  can 
therefore  be  dispensed  with  in  the  latter,  or  irrigation  in  the 
former.  Both  have  their  proper  place  in  both  regions;  but 
from  special  causes  underdrainage,  as  has  already  been  stated. 


236  SOILS. 

should  be  widely  used  in  irrigation  countries  to  prevent  the 
injuries  otherwise  but  too  likely  to  arise  from  over-irrigation 
(see  chap.  12,  p.  231). 

Winter  Irrigation. — In  many  regions  where  irrigation  is 
desirable  but  not  absolutely  necessary  in  ordinary  seasons,  or 
where  irrigation  water  is  scarce  in  summer,  much  advantage 
is  gained  by  insuring  thorough  saturation  of  the  land  during 
the  latter  part  of  winter,  especially  when  spring  or  summer 
crops  are  to  be  sown.  The  not  inconsiderable  time  required 
for  water  to  reach  its  permanent  level  or  the  country  drainage 
in  most  soils,  often  insures  the  retention  of  a  certain  surplus 
over  what  the  soil  can  permanently  hold,  within  the  period 
when  it  can  be  utilized  by  growing  crops;  whose  roots  more- 
over are  more  likely  to  penetrate  deeply  in  land  where  there 
is  a  steady  increase  of  moisture  as  they  descend,  than  when 
the  contrary  condition  is  encountered.  The  use  of  winter 
Hood-waters  to  saturate  the  land  is  therefore  in  many  cases  the 
saving  clause  for  a  dry  season. 

METHODS   OF  IRRIGATION.1 

The  manner  in  which  irrigation  water  is  supplied  to  land 
and  especially  to  growing  crops  exerts  such  a  potent  influence 
not  only  upon  the  welfare  of  the  plants  but  also  upon  the  condi- 
tion of  the  land,  that  a  brief  discussion  of  this  topic  seems 
necessary. 

The  following  methods  are  in  use  to  a  greater  or  less  ex- 
tent: 

1.  Surface  sprinkling. 

2.  Flooding. 

A.  By  lateral  overflow  from  furrows  or  ditches. 

B.  By  the  "  check  "  system. 

3.  Furrow  irrigation. 

4.  Lateral  seepage  from  ditches. 

5.  Basin  irrigation. 

6.  Irrigation  from  underground  pipes. 

1  Only  a  general  outline  of  the  principles  of  this  subject  is  given  in  this  volume; 
special  works  must  be  consulted  for  working  details.  Among  these  the  volume  by 
King  on  "  Irrigation  and  Drainage "  gives  probably  the  most  comprehensive 
presentation  of  the  subject  for  both  humid  and  arid  climates.  Also  bulletins  of 
the  U.  S.  Dep't  of  Agriculture. 


THE  WATER  OF  SOILS. 


257 


Surface  Sprinkling. — This  method  seems  to  be  the  closest 
imitation  of  the  natural  rainfall ;  and  yet  it  is  in  practice  about 
the  most  wasteful  and  least  satisfactory  of  all.  It  is  difficult  of 
application  on  any  large  scale,  from  obvious  causes;  on  the 
small  scale,  in  gardens  and  on  lawns,  its  disadvantages  become 
amply  apparent.  As  usually  practiced,  from  a  rose  spout  or 
spray  nozzle,  the  water  falls  much  more  abundantly  than  in 
the  case  of  any  desirable  rain,  within  the  short  time  allowed  by 
the  patience  of  the  operator.  If  continued  for  a  sufficient 
length  of  time  to  soak  the  soil  to  the  desirable  depth,  it  com- 
pacts the  surface  of  the  ground  so  as  to  render  subsequent  till- 
age indispensable.  To  avoid  this,  amateur  gardeners  usually 
restrict  the  time  of  application,  repeating  the  same  at  frequent 
intervals,  sometimes  daily.  The  result  is  that  the  very  slight 
penetration  of  the  water  either  fails  to  reach  the  absorbent 
roots,  so  that  it  is  of  little  use  to  them,  and  is  evaporated 
by  the  next  day's  sun  or  wind ;  or  else  it  tends  to  draw  the 
roots  close  to  the  surface,  where,  unless  the  application  of 
•water  is  actually  made  daily,  they  are  sure  to  suffer  from  the 
first  intermission  of  the  daily  dose.  In  actual  practice  the 
sprinkling  method  is  therefore  both  inefficient  and  wasteful 
of  water,  and  exposes  the  plants  to  grave  injury  from  any 
cessation  of  the  water  supply. 

Flooding  presupposes  land  either  level  or  only  slightly  slop- 
ing naturally,  or  rendered  so  artificially ;  usually  by  means  of 
the  plow  and  horse  scraper. 

Flooding  by  lateral  overflow  from  large  furrows,  or  ditches, 
is  very  commonly  practiced  where  the  water  supply  is  abundant 
and  large  areas,  such  as  alfalfa  or  grain  fields,  are  to  be  irri- 
gated. The  overflow  is  regulated  by  portable  check-boards, 
proceeding  from  the  highest  points  to  the  lowest,  and  leaving 
each  temporary  dike  in  place  until  the  ground  is  adequately 
soaked  or  the  water  reaches  the  next  furrow  below.  In  heavy 
ground  the  operation  may  have  to  be  repeated  to  insure  proper 
depth  of  percolation. 

Clicck  -flooding  necessitates  more  careful  leveling,  and  the 
throwing  up  of  small  dikes,  either  temporary  or  permanent. 
The  costliness  of  the  earth-work  restricts  the  use  of  this 
method  materially,  and  the  inconvenience  caused  in  tillage  by 


238  SOILS. 

the  dikes  is  objectionable,  especially  in  large-scale  culture. 
For  the  case  of  alfalfa  fields,  which  remain  permanently  set 
for  a  number  of  years,  it  is  however  the  largely  preferred 
method.  In  the  case  of  field  cultures,  the  consolidation  of  the 
surface  that  follows  flooding  on  the  heavier  soils  renders  sub- 
sequent tillage  necessary  in  all  but  very  sandy  soils ;  and  hence 
it  should  always  precede  broadcast  sowing. 

One  disadvantage  of  the  surface-flooding  system  is  the  slow 
penetration  of  the  water  caused  by  the  resistance  of  the  air  in 
the  soil  to  downward  displacement;  its  buoyancy  acting  di- 
rectly contrary  to  the  percolation  of  the  water.  In  close- 
grained,  heavy  soils  this  objection  is  very  serious,  on  account 
of  the  loss  of  time  involved  when  the  irrigator's  time  is  limited. 
On  sandy  lands  the  air  bubbles  up  quite  livelily  at  first,  but  this 
soon  ceases  and  the  air  is  compelled  to  escape  sideways  as  best 
it  can. 

Furrow  Irrigation. — By  this  method  it  is  intended  to  soak 
the  land  uniformly  by  allowing  the  water  to  flow  through  fur- 
rows drawn  3  to  8  feet  apart,  with  a  gentle  slope  from  the 
supply  or  head  ditch ;  the  flow  being  continued  until  the  water 
has  reached  the  far  end  of  the  furrows,  or  longer  according  to 
the  nature  of  the  soil,  especially  if  another  ditch  to  receive  the 
surplus  flow  lies  below.  The  furrows  should  subsequently  be 
closed  by  means  of  the  plow  or  cultivator;  but  even  if  left 
open  they  are  much  less  a  source  of  waste  by  evaporation  than 
would  be  a  flooded  surface.  The  water  thus,  in  the  main,  soaks 
downward  and  only  reaches  the  surface  by  capillary  rise,  so 
that  the  land  between  the  furrows  is  not  sensibly  compacted 
when  the  furrows  have  been  made  deep  enough.  Evidently 
this  is  a  much  more  rational  procedure  than  surface  flooding, 
as  it  tends  to  leave  most  of  the  surface  in  loose  tilth,  while 
penetrating  to  much  greater  advantage,  because  -of  the  ready 
escape  of  the  air  from  the  soil.  It  is  the  system  naturally  and 
almost  exclusively  used  in  truck  gardens  and  orchards,  and 
generally  where  crops  are  grown  in  drills  or  rows  sufficiently 
far  apart  to  permit  of  cultivation. 

The  figure  annexed l  shows  the  manner  in  which  water 
sinks  and  spreads  from  furrows  of  various  depths  and  widths, 

1    Published  by  permission  of  the  Department. 


THE  WATER  OF  SOILS. 


239 


Furrows  6  inches  deep  in  Heavy  Loam    Soil 


Narrow  and  Wide  Furrows  in  Sandy  Loam  Soil 


W/e 


A 


Furrows  5  and  10  inches  deep  in  Sandy  Loam  Soil 

Water  running, in  eac/>fseren  hours 


FIG.  43.— Profiles  of  Water  penetration  in  Furrow  Irrigation. 


240 


SOILS. 


as  actually  observed  in  the  work  of  the  Irrigation  Division  of 
the  U.  S.  Dep't  of  Agriculture,  under  the  direct  supervision 
of  Prof.  R.  H.  Loughridge  of  the  California  Station.  The 
mode  of  percolation  is  shown  for  two  soils,  a  heavy  loam  and 
a  sandy  one,  both  in  the  vicinity  of  Riverside,  Cal. 

The  upper  section  shows  the  variation  in  penetration  in  one 
and  the  same  soil  with  the  same  kind  of  furrow,  the  broken 
line  indicating  the  cessation  of  the  flow  in  the  furrows;  after 
which  there  was  a  still  farther  penetration  of  the  water  to  from 
6  to  9  inches  deeper. 

The  second  section  from  above  shows  the  percolation  of  the 
water  respectively  in  wide  and  narrow  furrows  of  the  same 
depth.  It  is  evident  at  a  glance  how  much  more  effective  is 
the  wide  furrow  in  utilizing  the  limited  time  during  which  the 
irrigator  usually  has  the  flow  at  his  command. 

The  third  section  shows  several  practically  important  points 
in  favor  of  the  wide  and  deep  instead  of  narrow  and  shallow 
furrow.  It  is  seen  that  in  doubling  the  width  and  depth,  the 
penetration  has  also  nearly  doubled.  Moreover,  it  is  seen  that 
in  the  deep  furrow  the  water  has  not  in  the  course  of  seven 
hours  reached  the  surface  at  all,  being  still  six  inches  away;  so 
that  in  view  of  the  diminishing  ratio  of  capillary  ascent,  it 
probably  would  not  have  reached  the  edge  of  the  furrow,  at 
the  surface,  in  less  than  thirty  hours.  Thus  all  surface  evapo- 
ration, which  oftentimes  causes  the  loss  of  50  %  of  the  water 
entering  the  shallow  furrows,  would  be  prevented ;  and  a  dry 
furrow-slice  might  be  turned  into  the  furrow  immediately  after 
the  cessation  of  the  water-flow,  effectually  obviating  the  need 
of  subsequent  tillage  also.  The  cost  of  the  latter,  together 
with  the  saving  in  water,  and  increased  efficiency  of  the  water 
by  deeper  penetration,  will  much  more  than  offset  the  addi- 
tional cost  and  trouble  of  plowing  deeper  furrows. 

There  is  therefore  every  reason  for  doing  away  with  the 
wasteful,  easy-going  practice  of  irrigating  in  numerous  shal- 
low furrows,  by  which  the  irrigator  loses  up  to  half  of  the 
water  paid  for,  by  evaporation ;  is  compelled  to  wait  for  the 
soaked  surface  to  dry  before  being  able  to  turn  back  a  furrow- 
slice  into  the  furrows  to  prevent  the  drying-out  of  their  mois- 
ture; and  by  losing  penetration  of  the  water,  is  obliged  to 


THE  WATER  OF  SOILS.  24! 

irrigate  again  within  a  much  shorter  time  than  will  be  neces- 
sary if  deep-furrow  irrigation  be  used. 

A  similar  experiment  with  deep  and  shallow  furrows  was 
made  at  the  Southern  California  station  near  Pomona  in  1901, 
as  reported  in  Bulletin  138  of  the  California  Station.  The 
results  as  far  as  they  went  were  precisely  similar,  and  upon 
the  basis  of  these  the  writer  earnestly  advocated  deep-furrow 
irrigation,  and  had  the  satisfaction  of  seeing  it  strongly 
approved  by  orange-growers  at  Riverside  and  elsewhere,  by 
putting  it  into  practice. 

In  addition  to  the  saving  and  better  utilization  of  the 
water  used,  this  mode  of  application  has  the  advantage  of 
preventing  the  roots  from  coming  too  near  the  surface;  it  will 
also  largely  eliminate  "  irrigation  hardpan  "  or  plowsole. 

The  results  produced  by  long-continued  shallow  plowing  and 
irrigation  in  shallow  furrows  is  well  illustrated  in  the  last  of 
the  irrigation  profiles,  which  shows  the  observations  made  on 
the  same  land  as  the  others,  but  where  rational  cultivation  and 
deep-furrow  irrigation  had  not  yet  been  introduced.  It  will 
be  seen  that  after  applying,  and  of  course  paying  for,  the 
water  for  three  days,  its  average  penetration  was  only  about 
eighteen  inches;  so  that  the  trees  of  the  orchard  received  very 
little  benefit,  and  were  supposed  to  be  needing  fertilization 
when  in  fact  they  were  simply  suffering  from  lack  of  water 
at  the  lower  roots. 

One  somewhat  unexpected  point  is  shown  by  these  dia- 
grams, viz.,  the  slight  sidewise  penetration  of  the  water;  the 
wetted  areas  having  a  nearly  vertical  lateral  outline.  This 
means,  of  course,  that  unless  the  furrows  run  very  near  the 
trees  of  an  orchard,  the  soil  immediately  beneath  the  trees 
will  remain  dry;  thus  inducing  the  roots  to  spread  sideways 
and  losing  depth  of  penetration  and  soil.  It  will  be  noted 
especially  in  the  lower  figure  that  here  again  the  deep  furrow 
offers  a  material  advantage  over  the  shallow,  the  sidewise 
spread  being  much  more  pronounced  than  in  the  shallow  fur- 
row alongside. 

Distance  Between  Furrows  and  Ditclies. — The  distance  be- 
tween the  furrows  must,  of  course,  be  proportioned  to  the 
readiness  with  which  the  water  penetrates,  being  less  as  the 
land  is  of  closer  texture.  The  distance  between  head  ditches 
16 


242  SOILS. 

must,  on  the  contrary,  vary  in  the  opposite  sense,  since  if  these 
are  too  far  apart,  the  water  near  the  head  ditch  will  in  sandy 
lands  be  wasting  into  the  subdrainage  before  the  end  of  the 
furrows  is  reached ;  so  that  the  distribution  will  be  very  un- 
even. The  great  differences  observed  between  crops,  and  es- 
pecially trees,  below  and  above  the  head  ditches,  are  mainly  due 
to  this  unevenness  in  water  distribution,  caused  by  too  great 
distance  between  successive  head  ditches.  Each  farmer  must 
himself,  however,  determine  by  actual  trial  the  proper  dis- 
tances between  ditches  as  well  as  furrows,  for  his  particular 
case;  since  everything  depends  upon  the  rapidity  with  which 
water  will  penetrate  the  soil  and  subsoil.  Actual  tests  to  de- 
termine this  point *  should  be  the  first  step,  before  laying  off 
the  system  of  ditches  as  well  as  furrows.  It  not  uncom- 
monly happens  that  the  failure  to  do  this  at  first,  compels  a 
subsequent  total  change  of  arrangements  in  this  respect.  (See 
page  253  below). 

Thus  while  in  some  very  pervious  land  furrows  may  be  six  or  even 
eight  feet  apart,  in  other  cases,  in  certain  finely  pulverulent  or  silty 
soils  such  as  the  "  dust  soils  "  described  in  a  former  chapter ;  (see  chapter 
6,  p.  104),  furrows  drawn  three  feet  apart  may  fail  to  allow  the  water  to 
penetrate  so  as  to  prevent  grain  on  the  middle  foot  from  suffering  from 
drought  after  the  water  has  run  for  twenty-four  hours. 

Irrigation  by  lateral  Seepage. — Is  in  reality  a  mere  modifi- 
cation of  furrow  irrigation,  practiced  in  the  case  of  lands  very 
readily  permeable,  and  where  water  is  abundant.  The  fields 
are  laid  off  in  "  lands  "  twelve  to  twenty-five  feet  wide,  with 
a  deep  furrow  or  narrow  ditch  between,  from  which  water 
percolates  in  a  short  time  so  as  to  overlap  from  the  two  sides. 
In  this  case  sometimes  the  water  does  not  reach  the  surface 
visibly  at  all ;  a  very  great  advantage  where  alkali  exists,  as 
surface  evaporation,  and  the  consequent  accumulation  of 
alkali,  is  thus  effectually  prevented;  while  deep  rooting  is 
favored  to  the  utmost. 

1  Such  tests  can  be  readily  made  by  any  one,  by  digging  a  pit  to  four  or  five  feet 
depth,  and  supplying  water  to  a  shallow  basin  dug  into  the  surface  8  to  12  inches 
distant  from  the  vertical  wall  of  the  pit.  The  descent  of  the  water  is  then  readily 
observed  on  the  vertical  side  of  the  pit  nearest  to  the  water  basin.  Preliminary 
tests  with  soil  probe  (see  chap.  10,  p.  }iJJ. 


THE  WATER  OF  SOILS.  243 

Basin  Irrigation. — In  this  method  of  irrigation,  practiced 
only  in  the  case  of  trees  and  sometimes  vines,  and  when  water 
is  scarce,  a  wide  circular  furrow  or  basin  is  excavated  around 
each  trunk  and  water  is  run  either  from  one  to  the  other,  or 
sideways  from  a  furrow  laid  along  the  rows.  The  \vater 
thus  applied  of  course  percolates  immediately  around  the  trunk 
first,  and  in  practice  is  found  to  follow  also  the  large  roots; 
so  that  it  goes  precisely  where  it  is  most  wanted,  besides  form- 
ing a  vertical  body  of  moist  soil  reaching  to  considerable  depth, 
where  it  is  most  desirable  that  the  root  system  should  follow. 
By  this  deep  penetration  to  natural  moisture  in  the  depths  of 
the  soil,  comparatively  small  quantities  of  water  produce  very 
marked  effects. 

On  the  same  principle,  the  grape  vines  which  bear  some  of 
the  choicest  raisins  of  Malaga  on  the  arid  coastward  slopes, 
are  made  to  supply  themselves  with  moisture,  without  irriga- 
tion, by  opening  around  them  large,  funnel-shaped  pits,  which 
remain  open  in  winter  so  as  to  catch  the  rain,  causing  it  to 
penetrate  downward  along  the  tap-root  of  the  vine,  in  clay 
shale  quite  similar  to  that  of  the  California  Coast  Ranges,  and 
like  the  latter  almost  vertically  on  edge.  Yet  on  these  same 
slopes  scarcely  any  natural  vegetation  now  finds  a  foot-hold. 

Similarly  the  "  ryats  "  of  parts  of  India  water  their  crops 
by  applying  to  each  plant  immediately  around  the  stem  such 
scanty  measure  of  the  precious  fluid  as  they  have  taken  from 
wells,  often  of  considerable  depth,  which  form  their  only 
source  of  water-supply.  Perhaps  in  imitation  of  these,  an  in- 
dustrious farmer  has  practiced  a  similar  system  on  the  high 
benches  of  Kern  River,  California,  and  has  successfully  grown 
excellent  fruit  for  years,  on  land  that  would  originally  grow 
nothing  but  cactus.  Sub-irrigation  from  pipes  has  been  applied 
in  a  similar  manner. 

A  combination  of  the  furrow-  and  basin-irrigation  system  is 
sometimes  practiced  in  southern  California  by  drawing  the 
furrow  so  as  to  bring  the  tree  within  a  square,  one  side  of 
which  is  left  closed.  The  same  result  may  be  accomplished 
by  plowing  cross  furrows  at  right  angles  near  the  tree  and 
then  placing  checkboards  so  as  to  force  the  water  along  the 
rows,  zigzagging,  on  three  sides. 

The   basin    irrigation    of    orchards    was    originally    largely 


244  SOILS. 

practiced  in  California,  but  has  now  been  mostly  abandoned 
for  furrow  irrigation.  The  latter  has  been  adopted  partly 
because  it  requires  a  great  deal  less  hand-labor,  partly  under 
the  impression  that  the  whole  of  the  soil  of  the  orchard  is  thus 
most  thoroughly  utilized;  partly  also  because  of  the  injurious 
effect  upon  trees  produced  at  times  by  basin  irrigation. 

The  explanation  of  such  injurious  effects  is,  essentially, 
that  cold  irrigation  water  depresses  too  much  the  temperature 
of  the  earth  immediately  around  the  roots,  and  thus  hinders 
active  vegetation  to  an  injurious  extent,  sometimes  so  as  to 
bring  about  the  dropping  of  the  fruit.  This  of  course  is  a 
very  serious  objection,  to  obviate  which  it  might  be  necessary 
to  reservoir  the  water  so  as  to  allow  it  to  warm  before  being 
applied  to  the  trees.1  In  furrow-irrigation  the  amount  of 
soil  soaked  with  the  water  is  so  great  that  the  latter  is  soon 
effectually  warmed  up,  besides  not  coming  in  contact  too  in- 
timately with  the  main  roots  of  the  tree ;  along  which  the  water 
soaks  very  readily  when  applied  to  the  trunk,  thus  affecting 
their  temperature  much  more  directly.  It  is  for  the  farmer  to 
determine  which  consideration  should  prevail  in  a  given  case. 
If  the  water-supply  be  scant  and  warm,  the  most  effectual  use 
that  can  be  made  of  it  is  to  apply  it  immediately  around  the 
tree,  in  a  circular  trench  dug  for  the  purpose.  When  on  the 
contrary,  irrigation  water  is  abundant  and  its  temperature  low, 
it  may  be  preferable  to  practice  furrow  irrigation,  or  possibly 
even  flooding. 

As  to  the  supposed  more  complete  use  of  the  soil  under  the 
latter  two  methods,  it  must  be  remembered  that  while  this  is 
the  case  in  a  horizontal  direction,  if  irrigation  is  practiced  too 
copiously  under  the  shallow-furrow  system,  it  may  easily  hap- 
pen that  the  gain  made  horizontally  is  more  than  offset  by  a 
corresponding  loss  in  the  vertical  penetration  of  the  root- 
system.  This  is  amply  apparent  in  some  of  the  irrigated 
orange  groves  of  southern  California,  where  the  fine  roots  of 
the  trees  fill  the  surface  soil  as  do  the  roots  of  maize  in  a 
corn  field  of  the  Mississippi  States;  so  that  the  plow  can  hardly 
be  run  without  turning  them  up  and  under.  In  these  same 
orchards  it  will  often  be  observed,  in  digging  down,  that  at  a 
depth  of  a  few  feet  the  soil  is  too  water-soaked  to  permit  of 

1  See  below,  chap.  17. 


THE  WATER  OF  SOILS.  245 

the  proper  exercise  of  the  root-functions,  and  that  the  roots 
existing  there  are  either  inactive  or  diseased.  That  in  such 
cases  frequent  irrigation  and  abundant  fertilization  alone  can 
maintain  an  orchard  in  bearing  condition,  is  a  matter  of 
course;  and  there  can  be  no  question  that  a  great  deal  of  the 
constant  cry  for  the  fertilization  of  orchards  in  the  irrigated 
sections  is  due  quite  as  much  to  the  shallowness  of  rooting 
induced  by  over-irrigation,  as  to  any  really  necessary  exhaus- 
tion of  the  land.  When  the  roots  are  induced  to  come  to  and 
remain  at  the  surface,  within  a  surface  layer  of  eighteen  to 
twenty  inches,  it  naturally  becomes  necessary  to  feed  these 
roots  abundantly,  both  with  moisture  and  with  plant-food. 
This  has,  as  naturally,  led  to  an  overestimate  of  the  require- 
ments of  the  trees  in  both  respects.  Had  deep  rooting  been 
encouraged  at  first  in  the  deep  soils  of  the  southern  "  citrus 
belt,"  instead  of  over-stimulating  the  growth  by  surface  fer- 
tilization and  frequent  irrigation,  some  delay  in  bearing  would 
have  been  compensated  for  by  less  of  current  outlay  for  fer- 
tilizers, and  less  liability  to  injury  from  frequently  unavoid- 
able delay,  or  from  inadequacy,  of  irrigation. 

Irrigation  b\  Underground  Pipes. — Where  economy  in  the 
use  of  irrigation  water  is  a  pressing  requirement,  its  distribu- 
tion through  underground  pipes  affords  the  surest  mode  of 
accomplishing  that  end,  in  connection  with  the  application  of 
the  water  in  accordance  with  the  principles  just  discussed. 
The  enormous  saving  of  water  effected  by  its  conveyance  in 
cement-lined  ditches  or  concrete  pipes,  as  compared  with  earth 
ditches,  if  additionally  combined  with  its  application  to  in- 
dividual trees  or  vines,  presents  the  maximum  of  economy 
that  can  be  effected.  The  actual  use  of  this  method  is  unfor- 
tunately limited  in  practice  by  the  high  first  cost  of  piping: 
but  as  its  use  renders  unnecessary  the  digging  of  basins  and 
plowing  of  furrows  and  their  subsequent  closing-up,  it  is  when 
once  established  by  far  the  cheapest  system,  both  as  to  the  use 
of  water  and  of  labor. 

The  best  results  of  this  system  are  undoubtedly  achieved  by  the 
use  of  iron  pipes  for  the  distribution  in  field  and  orchard,  whatever  may 
be  the  material  used  for  the  main  conduits.  The  use  of  concrete  and 
tile  in  small  sizes  proves  in  the  end  very  expensive,  because  of  frequent 


246  SOILS. 

breakage,  and  leakage  due  to  varying  pressure  in  the  supply  pipes  or 
reservoirs ;  as  well  as  from  even  slight  earthquake  tremors,  undermining 
by  water  or  by  the  burrowing  of  animals,  and  many  other  accidents 
which  do  not  affect  an  iron  pipe  system.  The  pipes  must  in  any  case, 
of  course,  be  laid  deep  enough  to  be  out  of  reach  of  the  deepest  tillage  ; 
therefore  not  less  than  one  foot,  and  preferably  eighteen  inches.  A 
proper  construction  of  the  outlets,  permitting  of  exact  regulation  of  the 
flow  and  ready  operation  from  above  ground,  as  well  as  preventing 
their  being  clogged  by  earth,  rust,  roots  or  burrowing  animals,  insects 
etc.,  is  of  course  of  the  greatest  importance.  A  variety  of  devices  for 
this  purpose  is  already  on  the  market. 

QUALITY  OF  THE  IRRIGATION  WATER. 

Saline  Waters. — Considering  the  large  amount  'of  water 
annually  used  in  irrigation,  among  the  most  needful  precau- 
tions to  be  observed  by  the  irrigator  is  in  the  testing  of  the 
quality  of  his  water-supply.  First  among  the  points  to  be 
noted  is  the  possible  content  of  soluble  "  alkali  "  salts.  While 
in  most  cases  what  is  called  the  "  rise  of  the  alkali  "  is  due  to 
the  salts  already  contained  in  the  soil  and  subsoil,  in  but  too 
many  the  evil  is  either  brought  about,  or  greatly  aggravated, 
by  the  excessive  saline  contents  of  the  water  used  in  irrigation. 
The  effects  of  the  use  of  saline  irrigation  water  (containing 
in  this  case  about  100  grains  per  gallon,  or  1700  parts  per 
million)  are  shown  in  the  accompanying  plate.  The  predom- 
inant ingredients  of  these  alkali  salts  were  common  salt  and 
carbonate  of  soda.  In  the  lands  near  Corona,  Cal.,  where  this 
case  was  observed,  the  original  alkali-content  of  the  soil  was 
about  2500  pounds  per  acre  in  four  feet  depth,  and  had  been 
just  quadrupled,  with  the  results  shown;  viz.,  complete  de- 
foliation of.  the  orange  trees,  while  on  the  same  land,  where 
the  trees  had  been  irrigated  with  good  artesian  water,  the 
orchard  was  in  fine  condition. 

.  Limits  of  Salinity. — It  is  not  easy  to  assign  a  definite  limit 
of  mineral  content  beyond  which  water  should  be  considered 
unfit  for  irrigation  purposes;  partly  because  of  the  differences 
in  the  kind  of  the  mineral  salts,  partly  because  the  nature  of 
the  soil  and  the  amount  of  water  at  command,  materially  in- 
fluence its  availability. 


THE  WATER  OF  SOILS. 


247 


248  SOILS. 

Forty  grains  per  gallon  is  usually  assigned  as  the  limit  for 
potable  as  well  as  irrigation  waters.  But  if  most  or  the  whole 
of  such  mineral  contents  should  consist  of  the  carbonates  and 
sulfates  of  lime  and  magnesia,  the  water  while  unsuitable  for 
domestic  use  may  be  perfectly  available  for  irrigation,  since 
these  salts  are  either  beneficial  or  harmless  in  the  amounts 
likely  to  be  introduced  by  the  water.  But  if  most  or  the  whole 
of  such  forty  grains  should  consist  of  "  alkali  salts  "  proper, 
viz.,  the  sulfates,  chlorids  and  carbonates  of  potash  and  soda, 
or  if  they  should  contain  even  small  amounts  of  the  chlorid 
and  magnesium,  they  might  render  the  water  either  wholly 
unsuitable  for  irrigation,  or  if  used  it  would  be  needful  to 
take  the  mineral  content  into  consideration,  by  regulating  its 
application  accordingly. 

It  has  been  found  in  California  that  practically  the  upper 
limit  of  mineral  content  for  irrigation  water  under  the  ordinary 
practice  lies  below  seventy  grains  per  gallon  in  all  cases;  for 
when  this  strength  is  reached,  even  though  such  water  may 
bathe  the  roots  of  almost  any  plant  with  impunity,  yet  acci- 
dental concentration  by  evaporation  is  so  certain  to  happen, 
that  injury  to  crops  is  practically  almost  unavoidable. 

In  South  Dakota  and  other  parts  of  the  American  semi-arid  region, 
waters  containing  seventy  grains  and  even  more  of  alkali  salts  per 
gallon  are  annually  used  during  the  short  irrigation  season.  This  can 
be  done  harmlessly  because  the  aggregate  amount  used  is  only  small, 
and  the  more  abundant  rainfall  of  that  region  annually  washes  the  salts 
out  of  the  soil.  But  where  almost  the  full  amount  of  water  required 
by  crops  must  be  supplied  by  irrigation,  the  total  amount  of  salts  thus 
introduced  would  speedily  render  the  land  uncultivable. 

According  to  the  observations  of  Means  and  other  explo- 
rers 1  of  the  U.  S.  Dep't  of  Agriculture,  waters  of  much 
higher  mineral  content  are  used  for  irrigation  both  in  Egypt 
•and  in  the  Saharan  region,  some  going  as  high  as  8000  parts 
per  million,  or  214  grains  per  gallon.  The  cultivators  are 
said  to  be  very  skilful  in  the  use  of  these  waters,  applying 
them  only  to  plants  of  known  resistance,  and  in  certain  ways. 
These  ways  include  doubtless  a  good  deal  more  time  and  pa- 

1  Bull.  No.  21,  Bureau  of  Soils  ;  also  circular  No.  10,  ibid. 


THE  WATER  OF  SOILS.  249 

tience  than  American  irrigators  are  ordinarily  willing  to  be- 
stow upon  their  work.  Much  depends  of  course  not  only 
upon  the  character  of  the  salts  in  the  water,  but  also  upon  the 
long  experience  had  in  the  old  irrigation  regions. 

Mode  of  using  Saline  Irrigation  U'aters. — The  fact  that 
abundant  growths  of  native  as  well  as  cultivated  plants  may 
sometimes  be  seen  on  the  margins  of  "  alkali  lakes  "  where 
water  of  over  a  hundred  grains  of  mineral  salts  per  gallon 
continuously  bathes  the  roots,  while  the  same  plants  perish  at 
some  distance  from  the  water's  edge,  points  the  way  to  the 
utilization,  in  emergencies,  of  fairly  strong  saline  waters;  viz., 
by  the  prevention  of  their  concentration  to  the  point  of  injury 
b\  evaporation.  It  is  clear  that  when  such  waters  are  used 
sparingly,  so  as  to  penetrate  but  a  few  feet  underground, 
whence  the  moisture  re-ascends  for  evaporation  at  the  surface, 
a  few  repetitions  of  its  use  will  accumulate  so  much  alkali  near 
the  surface  as  to  bring  about  serious  injury.  If,  on  the  other 
hand,  the  water  is  used  so  abundantly  that  the  roots  miy  be 
considered  as  being,  like  the  marginal  vegetation  of  alkali 
lakes,  bathed  only  by  water  of  moderate  strength,  no  such  in- 
jury need  occur;  and  what  does  accumulate  in  consequence  of 
the  inevitable  measure  of  evaporation  occurring  in  the  course 
of  a  season,  may  be  washed  out  of  the  land  by  copious  winter 
irrigation. 

This,  of  course,  presupposes  that  the  land,  as  is  mostly  the 
case  in  the  arid  region,  is  readily  drained  downwards  when  a 
sufficiency  of  water  is  used.  When  this  is  not  the  case,  c.  g., 
in  clay  or  adobe  soils,  or  in  those  underlaid  by  hardpan.  waters 
which  in  sandy  lands  could  have  been  used  with  impunity,  may 
become  inapplicable  to  irrigation  use. 

Apparent  Paradox. — The  prescription  to  use  saline  waters 
more  abundantl\  than  purer  ones,  in  order  to  avoid  injury 
from  alkali,  though  paradoxical  at  first  sight,  is  therefore 
plainly  justified  by  common  i^ense  as  well  as  by  experience,  in 
pervious  (sandy)  soils;  while  in  difficultly  permeable  cues. 
their  use  may  be  either  wholly  impracticable,  or  subject  to 
very  close  limitation. 

Sometimes  the  alternate  use  of  pure  and  salt-charged  water 
serves  to  eke  out  a  too  scant  supply  of  the  former.  Hut  in 


250 


SOILS. 


all  such  cases,  close  attention  to  the  measure  of  water  that  will 
wet  the  soil  to  a  certain  depth,  and  "  eternal  vigilance  "  with 
respect  to  the  accumulation  of  alkali  near  the  surface,  must  be 
the  price  of  immunity  from  injury.  In  all  cases  the  farmer 
should  know  how  much  of  alkali  salts  he  introduces  into  his 
land  with  the  irrigation  water,  and  watch  that  it  does  not  ap- 
proach too  closely,  or  exceed,  the  tolerance  of  his  crops  for 
alkali  salts,  as  given  in  chapter  26. 

Use  of  Drainage  Waters  for  Irrigation. — When  lands 
charged  with  alkali  salts  are  being  reclaimed  by  drainage,  the 
question  sometimes  arises  whether  the  drainage-water  may  not 
be  used  for  irrigation,  'lower  down.  This  of  course  depends 
entirely  upon  the  amount  of  alkali  in  the  water,  the  nature  of 
the  lands  to  be  irrigated,  and  the  manner  of  applying  it.  In 
the  Fresno  drainage-district  of  California  it  has  been  shown 
that  some  of  the  drainage-water  contains  not  more  than  25  to 
30  grains  per  gallon  of  objectionable  salts,  and  such  waters 
could  of  course  be  used  on  pervious  lands  with  the  precautions 
above  noted. 

"  Black  Alkali"  Waters. — As  regards,  however,  waters  con- 
taining any  large  proportion  of  carbonate  of  soda,  it  must  be 
remembered  that  even  very  dilute  solutions  of  salsoda  serve 
to  puddle  the  soil  and  thus  render  it  difficultly  tillable.  When 
such  waters  are  used  it  is  necessary  to  forestall  injury  either 
by  the  use  of  gypsum  in  the  reservoir  or  ditch,  or  by  annually 
using  on  the  land  a  sufficient  amount  of  gypsum  to  transform 
the  carbonate  of  soda  into  the  relatively  innocuous  sulfate. 

Variations  in  the  Saline  Contents  of  Irrigation  Waters. — 
When  irrigation  waters  are  derived  from  deep  wells,  there  is 
little  if  any  variation  of  their  saline  contents  to  be  expected, 
and  a  single  analysis  will  serve  permanently.  But  in  the  case 
of  relatively  shallow  wells,  from  which  the  water  must  be 
raised  by  pumping,  it  not  unfrequently  happens  that  after  a 
series  of  seasons  of  short  rainfall,  saline  waters  are  brought 
up  by  the  pump  and  may  seriously  injure  crops  and  orchards. 
Again,  in  the  case  of  streams  and  rivers  whose  flow  becomes 
very  small  in  summer,  the  saline  content  may  increase  to  sev- 
eral times  the  amount  carried  at  the  time  of  high  water. 
Both  kinds  of  cases  occur  in  southern  California,  in  Arizona,1 

1  Bull.  Ariz.  Exp't  Sta.  No.  44. 


THE  WATER  OF  SOILS.  251 

New  Mexico  and  other  states  of  the  arid  region.  The  Gila, 
Pecos  and  upper  Rio  Grande  are  cases  in  point,  and  to  a  cer- 
tain extent  the  Colorado  of  the  West. 

Muddy  Waters. — In  the  latter  as  well  as  other  streams  of 
Arizona,  there  is  another  point  which  sometimes  creates  diffi- 
culties to  the  irrigator,  together  with  some  current  expense. 
It  is  the  amount  of  silt  or  mud  carried  by  the  water,  which 
while  it  is  a  benefit  to  the  land  over  which  it  is  spread,  ("  warp- 
ing ")  as  in  the  classic  case  of  the  Nile,  often  clogs  the  irriga- 
tion ditches  to  such  an  extent  as  to  cause  considerable  incon- 
venience and  expense  in  cleaning  them  out.  This  is  especially 
the  case  in  the  streams  draining  pasture  lands  that  have  been 
overstocked,  and  where  the  destruction  of  the  natural  herbage 
allows  the  rain  water  to  run  off  rapidly,  at  first  forming  run- 
lets and  then  gullies  and  ravines  that  originally  were  simply 
cow-paths  leading  toward  the  watering  places.1  The  devasta- 
tion of  lands  thus  caused  in  Arizona  is  almost  as  great  as  that 
which  has  occurred  in  the  Cotton  states,  as  mentioned  above 
chap.  12,  p.  217. 

These  variations  in  the  character  of  the  irrigation  water 
must  of  course  be  watched  by  the  farmer  who  does  not  receive 
directly  from  mountain  streams,  or  from  deep  artesian  wells 
water  known  to  have  a  constant  content  of  saline  matter. 

THE  DUTY  OF  IRRIGATION  WATER. — The  amount  of  water 
thought  to  be  needed  for  the  production  of  satisfactory  crops 
varies  widely  in  different  regions,  ranging  all  the  way  from 
about  two  feet  to  as  much  as  eight  annually,  within  the  United 
States;  while  in  the  sugar-cane  fields  of  the  Hawaiian  Islands 
as  much  as  three  inches  per  week,  or  over  twelve  acre-feet  in 
the  course  of  the  year,  have  been  thought  to  be  beneficial,  if 
not  absolutely  required  for  the  best  crop  results. 

As  has  been  stated  above  (chap.  12.  p.  215),  the  rainfall 
limit  below  which  irrigation  becomes,  if  not  absolutely  essen- 
tial, at  least  a  highly  desirable  condition  for  the  safety  of 
crops,  is  usually  assumed  to  lie  at  about  20  inches  (500  mili- 
meters).  This  general  statement  is,  however,  subject  to  ma- 
terial modification  according  to  the  manner  in  which  the  rain- 
fall is  distributed.  Thus  in  central  Montana  with  24  inches 
of  rainfall  distributed  throughout  the  year,  irrigation  is  indis- 

1  Hull.  Arizona  Kxp't  Station  Nos.  2,  38. 


SOILS. 

pensable;  while  in  the  Santa  Clara  valley  of  central  California, 
with  an  average  rainfall  of  15  inches  falling  through  the 
winter  and  spring,  the  growth  of  all  ordinary  field  crops  has, 
for  fifty  years  not  failed  oftener  than  is  commonly  the  case  in 
the  humid  region  of  the  North  Central  states.  This  is  be- 
cause in  California  the  winter  and  spring  are  the  growing  sea- 
sons, while  the  rainless  summers  do  not  stand  in  the  way, 
for  crops  are  already  harvested;  and  the  deep  rooting  of  trees 
and  vines  provides  these  with  the  needful  moisture  from  the 
depths  of  the  substrata  (see  chap.  10,  pp.  163  to  173). 

It  would  thus  seem  that  twenty  inches  of  irrigation  water 
properly  applied  ought  to  be  sufficient  for  all  purposes,  when 
added  to  the  natural  rainfall,  which  is  rarely  entirely  absent. 
Yet  in  actual  practice  less  than  24  acre-inches  is  rarely  used, 
and  much  more  is  the  rule ;  72  to  96  ins.  being  sometimes  used 
in  Arizona.  Evidently  enormous  losses  occur  in  practice,  and 
it  is  of  the  utmost  importance  to  discover  the  causes  of  these. 

Causes  of  Loss. — Since  irrigation  water  is  commonly  mea- 
sured at  the  distributing  weirs,  loss  from  seepage  and  evapora- 
tion on  the  way  to  the  fields  is  an  obvious  source  of  an  over- 
estimate of  the  water  actually  supplied  to  the  farmer.  In 
sandy  districts  the  loss  thus  incurred  is  reliably  estimated  at 
nearly  50%  in  many  cases.  The  apparent  duty  of  the  water 
is  thus  at  once  reduced  to  half  its  effect,  and  four  instead  of 
two  feet  of  water  are  supposed  to  have  been  used,  and  are 
charged  for. 

Evaporation  resulting  from  surface  flooding  or  use  in  shal- 
low furrows  may,  again,  cause  the  loss  of  from  30  to  50% 
of  the  water  that  actually  reaches  the  land ;  so  that  in  the  lat- 
ter case,  between  seepage  and  evaporation  the  irrigator  may 
lose  the  effect  of  three-fourths  of  the  water  he  pays  for. 

Loss  b\  Percolation. — Finally,  the  water  may  be  wasted  on 
the  land  itself  in  leachy  soils  by  over-use,  /.  e. ,  it  may  percolate 
to  a  large  extent  beyond  the  reach  of  the  roots  when  the  flow 
is  continued  too  long;  as  will  always  be  the  case  when  the 
head  (supply)  ditches  are  laid  too  far  apart,  so  that  the  water 
may  be  wasting  into  the  country  drainage  just  below  the  upper 
ditch  long  before  the  water  in  the  furrow  reaches  the  lower 
one;  as  illustrated  in  the  upper  one  of  the  subjoined  diagrams. 


THE  WATER  OF  SOILS. 


253 


That  this  will  not  happen  when  the  head  ditches  are  nearer 
together,  is  shown  in  the  lower  diagram. 


HC40  DITCH  .,  FLUHt 


FIGS  46,  47. — Diagram  showing  loss  by  percolation  when  head  ditchers  are  too  far  apart. 

The  means  of  avoiding  the  mechanical  losses  have  already 
been  discussed,  and  may  be  summarized  thus :  tightening  of 
leaky  ditches;  use  of  water  in  deep  furrows;  and  ascertaining 
the  rapidity  of  percolation  (see  p.  242)  so  as  to  obtain  a 
proper  gauge  for  the  time  during  which  water  should  run,  and 
for  the  distances  at  which  head  ditches  or  furrows  should  be 
placed. 

The  importance  of  thus  diminishing  the  losses  of  water  is 
obvious  when  it  is  considered  that  if  the  duty  of  water  can  be 
reduced  to  twenty  instead  of  forty  or  fifty  acre-inches,  twice 
the  area  can  be  irrigated  with  the  same  amount  of  water,  or 
the  cost  of  water  correspondingly  reduced.  It  should  be  noted 
that  when  the  land  is  leachy  it  may  be  pure  waste  to  continue 
the  flow  beyond  a  few  hours;  but  the  irrigation  must  then  be 
more  frequently  repeated. 

EVAPORATION. 

.Alongside  of  and  supplementary  to  the  best  possible  utiliza- 
tion of  the  rainfall  and  irrigation  water,  the  prevention  of  un- 
necessary evaporation  has  to  be  considered.  Evaporation 
from  the  soil's  surface  implies  not  only  unnecessary  loss  of 
water  that  should  have  remained  for  the  use  of  the  crop,  but 


254  SOILS. 

also  the  depression  of  temperature  which,  as  a  rule,  is  un- 
favorable to  the  best  development  of  vegetation.  It  is  only 
in  case  of  extreme  stress  from  hot,  drying  wind  that  such 
evaporation  and  the  consequent  depression  of  the  temperature 
of  the  surface  soil  can  be  of  advantage  to  the  farmer. 

The  amount  of  water  evaporating  either  from  a  water-sur- 
face, or  from  a  wet  or  moist  soil,  varies  greatly  according  to 
the  climatic  conditions,  and  the  state  of  the  weather;  also  ac- 
cording to  the  condition  of  the  soil-surface.  There  are  damp 
climates,  and  days  or  periods  when,  the  air  being  nearly  sat- 
urated with  moisture,  evaporation  even  from  a  water-surface 
will  be  almost  insensible.  On'  the  other  hand,  with  dry  air 
and  a  high  temperature,  enormous  quantities  of  water  may  be 
evaporated  in  the  course  of  a  day.  The  evaporation  from 
water-surfaces  interests  deeply  those  who  supply,  as  well  as 
those  who  are  supplied  with,  water  from  storage  reservoirs; 
evaporation  from  the  soil-surface  interests  deeply  all  farmers, 
and  more  especially  irrigators  whose  water-supply  is  scanty, 
or  is  paid  for  by  them  by  measurement.  Light  rains,  as  well 
as  light  surface  irrigations,  may  at  times  evaporate  almost 
wholly  without  any  effect  save  a  lowering  of  the  temperature 
of  the  soil.  In  the  case  of  snow,  it  is  a  well-known  fact  in 
the  northern  arid  regions  that  a  light  snowfall  may  in  winter 
evaporate  entirely  without  imparting  any  liquid  moisture  to 
the  soil.  A  loss  of  50%  of  the  water  actually  brought  upon 
land  by  surface  irrigation  is  of  common  occurrence  in  some 
portions  of  the  irrigated  region. 

The  dependence  of  evaporation  upon  air-temperature  under 
conditions  otherwise  identical,  is  well  illustrated  by  the  ex- 
periments made  in  1004  by  S.  Fortier  1  on  the  Experiment 
Station  grounds  at  Berkeley,  California,  at  a  time  when  un- 
der the  influence  of  the  sea  breeze  the  average  saturation  of  the 
air  might  be  assumed  at  about  70%.  The  tests  were  con- 
ducted in  six  tanks  sunk  into  the  ground  so  as  to  place  the 
water-surfaces  on  a  level  with  it,  and  the  water-temperatures 
were  maintained  in  four  of  the  tanks  by  means  of  ice  or  heat- 
ing lamps.  The  results  are  shown  in  the  following  table : 

1  Progress  Report  on  Cooperative  Irrigations  in  Calif. ;  Cir.  No.  56,  Office  Exp't 
Stations. 


THE  WATER  OF  SOILS. 


255 


SUMMARY  OF  AVERAGE   WEEKLY   LOSSES    BY   EVAPORATION,   WITH    VARYING    TEM- 
PERATURES OF  WATER,  AT  BERKELEY,  CAL.,  IN  JULY  AND  AUGUST,  1904 


Temperature  of  water. 

Weekly 
evapora 
tion. 

Degrees  Fahrenheit  : 

cc.t.  . 

Inches. 

0.42 

yj  •>  
62.0  

O.77 

69.2  

1.^4. 

80.1  

1.o8 

89.2  

TQ2 

A  farther  illustration  is  given  in  the  subjoined  table,  show- 
ing maxima  and  mimima  of  monthly  evaporation,  as  well  the 
totals  of  one  (seasonal)  year,  in  three  California  localities 
where  the  air-saturation  is  considerably  below  that  at  Berkeley, 
ranging  in  summer  from  50%  to  20%  and  even  less  (at 
Calexico  in  the  Colorado  desert)  : 

SUMMARY  OF  EVAPORATION-LOSSES   FROM  WATER-SURFACES,  AT    POMONA,  TULARE, 
AND  CALEXICO,  CAL.,  FROM  JULY  I,  1903,  TO  JULY  31,  1904. 


Pomona. 

Tulare. 

Calexico. 

Month. 

Inches. 

Month. 

Inches. 

Month. 

Inches. 

Maximum.  ....... 

Aug.  1903 
Feb.  1904 

0.07 

'2-S7 
66.92 

July  1903 
Jan.  1904 

12-34 
1.46 
74.68 

July  1903 
Jan.  1904 

14.48 

4-39 
108.23 

Minimum  

Totals  for  year.  .  . 

Of  these  three  stations,  Pomona  is  located  within  reach  of 
the  ocean  winds,  but  distant  25  to  30  miles  from  the  shore. 
Tulare  is  situated  in  the  upper  San  Joaquin  valley,  far  in  the 
interior;  Calexico  is  in  the  southern  part  of  the  Colorado 
desert,  with  extremes  of  temperature  ranging  from  13°  Fahr. 
in  winter  to  120°  in  summer. 

Evaporation  in  nifTcrcnt  Climates. — The  following  table 
conveys  some  general  data  regarding  average  evaporation  from 
water-surfaces  in  different  climates.  Evaporation  from  the 
soil-surface  depends  largely,  of  course,  upon  the  mechanical 
condition  of  the  surface,  the  extent  to  which  it  is  wetted,  and 


256 


SOILS. 


the  rapidity  with  which  moisture  will  be  supplied  from  the 
subsoil  as  the  surface  dries.  A  field  plowed  into  rough  fur- 
rows will  evaporate  more  water  than  when  harrowed,  because 
of  the  larger  surface  exposed ;  and  a  harrowed  field  moderately 
compacted  by  rolling  will  lose  less  water  by  evaporation  than 
when  un-rolled,  other  things  being  equal.  On  the  other  hand, 
a  thoroughly  compacted  surface,  even  if  suffering  less  loss  at 
first  than  a  plowed  or  harrowed  field,  will  continue  to  lose 
moisture  longer  by  withdrawing  it  from  the  substrata  by  its 
superior  capillary  suction;  while  a  loose  surface,  once  dried 
out,  will  prevent  farther  loss  from  the  subsoil  very  effectually, 
as  stated  below. 


TABLE  SHOWING  EVAPORATION,  FROM  WATER-SURFACE  EXPOSED  IN  SHALLOW 
TANKS,  NEAR  WATER  OR  GROUND  SURFACE. 


Years. 

Inches. 

q 

17.80  (16.6  to  18.4). 

London,                  "        

14 

20.66 

Oxford                     "        

c 

71.04 

Munich    Germany     

24.00 

IO 

27.OQ 

Cambridge,  Massachusetts  

I 

;6.oo 

Syracuse,  New  York  ...    

I 

SO.  2O 

Logan,  Utah  

I 

C2.-3Q 

Tucson,  Arizona.  

I 

7S-8o 

Fort  Collins,  Colorado  

II 

41.00 

Fort  Bliss,  Texas  

I 

82.70 

4^  to  SO 

Sweetwater  Reservoir,  San  Diego,  California. 
Peking,  China  

I 

? 

57-6* 
18.80 

Demerara,  South  America  

•j 

1Z.I2 

Bombay,  Kast  India             

e 

82.28 

Petro-Alexandrowsk,  West  Turkestan  
Kimberley,  South  Africa  

? 

? 

96.40 
08.80 

Alice  Springs,  South  Australia  

? 

107.  t;o 

This  table,  the  data  for  which  are  taken  from  various 
sources,  exhibits  clearly  the  enormous  variations  in  evapora- 
tion in  different  countries,  and  even  in  localities  not  very  re- 
mote from  each  other.  The  low  evaporation  near  London  is 
doubtless  due  to  its  foggy  and  hazy  atmosphere,  but  it  is  not 
clear  why  Rothamsted  should  show  so  low  an  evaporation 
compared  with  Oxford.  Tropical  Demerara  stands  nearest  to 
Oxford  in  its  evaporation ;  Bombay  indicates  its  location  on 


THE  WATER  OF  SOILS.  257 

the  hot  and  arid  west  coast  of  India,  despite  its  nearness  to 
the  sea.  The  inland  localities  in  the  desert  regions  of  South 
Africa,  Australia  and  Western  Turkestan,  show  how  enormous 
may  be  the  losses  from  evaporation  of  irrigation  water,  unless 
the  latter  is  applied  with  special  care  for  their  prevention. 
Thus,  with  the  wasteful  methods  of  irrigation  prevailing  in 
portions  of  the  American  arid  region,  it  is  certain  that  in 
many  cases  50%  and  more  of  the  water  evaporates  before  it 
reaches  the  crops. 

Evaporation  from  Reservoirs  and  DiteJies. — The  evapora- 
tion from  water-surfaces  especially  may,  in  many  cases,  ex- 
ceed the  rainfall  of  the  year,  so  as  to  materially  diminish  the 
available  water-supply  in  reservoirs.  Thus  the  animal  evap- 
oration from  the  reservoir-lakes  forming  part  of  the  water- 
supply  of  the  city  of  San  Francisco,  ranges  from  40  to  50 
inches,  while  the  rainfall  averages  less  than  24  inches.  Were 
it  not,  then,  for  the  prevention  of  evaporation  by  a  covering  of 
dry  earth  during  summer,  no  moisture  would  remain  in  the 
ground  to  sustain  vegetation.  In  the  cool  coast  climate  of 
Berkeley,  Cal.,  directly  opposite  the  Golden  Gate  and  subject 
to  its  summer  fogs,  evaporation  from  a  water-surface  main- 
taining the  average  climatic  temperature  of  60°,  was  found 
to  be  y\  inch  during  the  month  from  the  middle  of  July  to  the 
middle  of  August,  1904.  But  at  the  high  temperatures  and 
low  degree  of  air-saturation  prevailing  in  the  great  interior 
valley,  or  in  the  Colorado  desert,  the  evaporation  from  water- 
surfaces  is  enormously  increased,  exceeding  even  the  figure 
given  in  the  table  for  Bombay.  Hence  the  great  importance  of 
preventing  all  avoidable  evaporation,  particularly  in  the  use  of 
irrigation  water. 

Prevention  of  Evaporation;  Protective  Snrfaee  Lover. — The 
loose  tilth  of  the  surface  which  is  so  conducive  to  the  rapid 
absorption  of  surface-water,  is  also,  broadly  speaking,  the  best 
means  of  reducing  evaporation  to  the  lowest  possible  point. 
For  while  it  is  true  that  the  (loccules  of  well-tilled  soil  permit 
of  the  ready  access  of  air.  and  therefore  of  evaporation,  it  is 
also  true  that  these  relatively  coarse  compound  particles  are 
incapable  of  withdrawing  capillary  moisture  from  the  denser 
soil  or  subsoil  underneath;  just  as  a  dry  sponge  is  incapable 


258  SOILS. 

of  absorbing  any  moisture  from  a  wet  brick,  while  a  dry 
brick  will  readily  withdraw  nearly  all  the  water  contained  in 
the  relatively  large  pores  of  the  sponge  (see  chap.  n).  A 
layer  of  loose,  dry  surface-soil  is  therefore  an  excellent  pre- 
ventive of  evaporation  of  the  moisture  from  soils,  and  may 
be  regarded  as  the  natural  and  most  available  means  to  be 
used  by  the  farmer,  both  for  the  prevention  of  evaporation 
and  to  moderate  the  access  of  excessive  heat  and  dryness  to 
the  active  roots. 

As  regards  the  desirable  thickness  of  this  protective  layer 
of  tilled  surface-soil,  it  should  be  kept  in  mind  that  in  the 
humid  region,  where  rain  can  be  expected  at  intervals  of  from 
one  to  three  weeks,  the  feeding  roots  may  usually  be  found 
within  a  few  inches  of  the  surface;  while  in  the  arid  region, 
where  irrigation  is  practiced  at  long  intervals  or  sometimes 
not  at  all,  so  that  no  water  enters  the  soil  oftener  than  from 
two  to  six  months,  the  roots  necessarily  vegetate  at  lower 
depths,  and  hence  the  protective  surface-layer  can,  and  should 
be,  of  greater  thickness,  to  prevent  the  penetration  of  excessive 
heat  and  dryness  during  the  long  interval. 

The  failure  to  appreciate  this  necessary  difference  often 
leads  to  heavy  losses  on  the  part  of  newcomers  to  the  arid 
region,  who  in  this  as  in  other  respects  are  apt  to  follow 
blindly  the  precepts  familiar  to  them  in  the  East,  until  taught 
better  by  sore  experience.  In  the  East  and  Middle  West  a 
depth  of  three  inches  is  considered  the  proper  one  for  the  pro- 
tective surface-layer;  and  in  the  case  of  maize  even  this  is 
considered  excessive  in  many  cases.  In  the  arid  region  this 
depth  should  be  at  least  doubled  where  irrigation  is  not  prac- 
ticed at  least  every  four  to  six  weeks ;  and  in  some  sandy  soils 
even  seven  and  eight  inches  is  not  too  much  for  effective 
protection. 

Illustrations  of  Effects  of  Surface  Tillage. — The  efficacy  of 
loose  surface  tilth  in  preventing  evaporation,  as  compared 
with  mere  superficial  scratching  or  with  the  total  omission  of 
cultivation,  is  well  exemplified  in  a  series  of  investigations 
conducted  on  this  subject  during  the  extremely  dry  season  of 
1898,  by  the  California  Experiment  Station;  the  seasonal  rain- 
fall having  during  that  year  been  on  an  average  from  one- 
third  to  one-half  onlv  of  the  usual  amount,  so  as  to  test  to  the 


THE  WATER  OF  SOILS. 


259 


utmost  the  endurance  of  all  growing  plants.  Some  of  the 
details  of  this  investigation  have  been  given  above  (p.  214)  in 
connection  with  the  question  of  moisture  requirements  of 
crops.  Loughridge 1  also  investigated  the  moisture  condi- 
tions in  adjacent  orchards  differently  treated  in  cultivation. 
In  one  of  these  cases  two  orchards  of  apricots  were  separated 
only  by  a  lane,  and  the  soil  identical ;  but  one  owner  had  omit- 
ted cultivation,  while  the  other  had  cultivated  to  an  extra  depth 
in  view  of  the  dry  season  apparently  impending.  The  results 
are  best  shown  by  the  plates  below,  showing  representative 
trees  and  the  annual  growth  made  by  each.  The  table  an- 
nexed shows  the  differences  in  the  moisture-content  of  the  two 
fields  to  the  depth  of  six  feet,  in  July : 

MOISTURE   IN   CULTIVATED  AND   UNCULTIVATED   LAND. 


Depth  in  soil. 

Cultivated. 

Uncultivated. 

Per  cent. 

Tons  per 
acre. 

Per  cent. 

Tons  per 
acre. 

First  toot  

6.4 
*8 

6.4 
6.5 
6.7 
6.0 

~67 

128 
116 
128 

!3° 

'34 

1  20 

~56 

4-3 
4.4 

3-9 
5-' 
34 

4-5 

4.2 

86 
88 
?S 

IOO 

68 
90 

512 

Second  foot  

Third  foot  

Fourth  foot  

Fifth  foot  

Sixth  foot  .                .... 

Total  for  six  foot  

The  difference  of  244  tons  per  acre  of  ground  shown  by  the 
analyses  is  quite  sufficient  to  account  for  the  observed  differ- 
ence in  the  cultural  result.  The  cause  of  this  difference  was 
that  in  the  uncultk'citcd  field  there  was  a  compacted  surface- 
layer  of  several  inches  in  thickness,  which  forcibly  abstracted 
the  moisture  from  the  substrata  and  evaporated  it  from  its 
surface;  while  the  loose  surface  soil  on  the  cultivated  ground 
was  unable  to  take  any  moisture  from  the  denser  subsoil. 

The  cultural  results  were  that  on  the  cultivated  ground  the 
trees  made  about  three  feet  of  annual  growth,  and  the  fruit 


Rep.  Calif.  F.xpt.  Sta.  for  1897-1)8,  p.  65. 


2GO 


SOILS. 


THE  WATER  OF  SOILS. 


261 


i"i«.  59. — New  Growth  and  fruit  on  Trees,  Cultivated  and  Uncultivated.     Creek  Bench  Land 

at  N  iles,  Cal. 


262  SOILS. 

was  of  good,  normal  size;  while  the  trees  in  the  uncultivated 
ground  made  barely  three  inches  of  growth,  and  the  fruit  was 
stunted  and  wholly  unsaleable.  It  may  be  added  that  when, 
instructed  by  the  season's  experience,  the  owner  of  the  "  un- 
cultivated "  orchard  cultivated  deeply  the  following  season, 
his  trees  showed  as  good  growtji  and  fruit  as  his  neighbor's. 

EVAPORATION   THROUGH    THE   ROOTS   AND   LEAVES   OF    PLANTS. 

Undesirable  as  is  the  evaporation  from  the  surface  of  the 
soil,  under  all  but  exceptional  conditions  the  evaporation  from 
the  leaves  of  plants  is  one  of  the  essential  functions  of  veg- 
etable development.  Not  only  because  water  serves  as  the 
vehicle  of  the  plant-food  absorbed  by  the  roots  and  to  be  or- 
ganized by  and  redistributed  from  the  leaves,  and  the  aeration 
occurring  in  the  latter  must  of  necessity  result  in  a  certain 
degree  of  evaporation;  but  largely  because  the  conversion  of 
liquid  water  into  vapor  serves  to  prevent  an  injurious  rise  of 
temperature  in  the  leaves  under  the  influence  of  hot  sunshine 
and  dry  air.  It  is  undoubtedly  for  the  latter  purpose  that 
the  greater  part  of  the  enormous  amount  of  water  required,  as 
above  stated  (chap,  n)  for  the  production  of  one  part  of 
dry  substance,  is  actually  used.  When  sufficient  water  to 
supply  the  required  evaporation  through  the  leaves  cannot  be 
brought  up  from  the  soil,  the  plant  begins  to  wilt ;  or  in  the 
case  of  some  plants  with  very  thin  and  soft  leaves  the  blade 
normally  begins  to  droop  during  the  hottest  hours  of  the  day; 
thus  escaping  excessive  exposure  to  the  sun's  rays,  and  re- 
covering their  turgor  later  in  the  afternoon. 

The  amount  of  water  actually  evaporated  from  orchard  trees  has  un- 
fortunately not  been  directly  determined,  the  investigations  made  in 
this  respect  having  borne  mainly  upon  forest  trees.  The  Austrian 
Forest  Experiment  Station  made  a  series  of  elaborate  investigations  on 
this  subject  in  1878,  and  the  following  data  (quoted  from  the  Report  • 
of  the  U.  S.  Dep't  of  Agriculture  for  1889)  convey  some  idea  of  the 
results. 

It  was  found  that  the  surface-areas  of  the  leaves  do  not  give  reliable 
results,  but  that  these  depend  very  largely  upon  the  thickness  (mass)  of 
the  leaves.  The  dry  weight  of  the  latter  was  found,  as  in  the  case  of 


THE  WATER  OF  SOILS.  263 

field  crops,  to  correspond  most  nearly  so  the  observations  made  directly. 
It  was  thus  found  that  e,  g.  birch  and  linden  transpired  during  their 
annual  period  of  vegetation  from  600  to  700  pounds  of/water  per  pound 
of  dry  leaves ;  oaks  200  to  300,  while  the  figures  for  ash,  beech  and 
maple  were  in  between.  On  the  other  hand  the  conifers — spruce,  flr 
and  pine — ranged,  under  the  same  conditions,  from  30  to  70  pounds 
of  water  only.  In  another  year,  these  figures  were  increased  for  decid- 
uous trees  to  from  500  to  1000,  the  conifers,  75  to  200  pounds.  This 
great  variability  indifferent  seasons,  together  with  other  elements  of 
uncertainty,  render  these  figures  only  roughly  approximate  ;  but  it  will 
be  noted  that  the  figures  for  deciduous  trees  are  in  general  of  the  same 
order  as  those  given  above  for  field  crops.  Assuming  the  evaporation 
for  citrus  trees  to  be  approximately  the  same  as  for  the  European  ever- 
green oak  (Q.  cerris)  viz.  500  pounds  per  pound  of  dry  matter,  and 
taking  the  weighings  made  by  Loughridge  of  the  leaves  of  a  *5 -year- 
old  orange  tree  at  Riverside  as  a  basis  (40  pounds  of  dry  leaves),  the 
water  evaporated  by  each  such  tree  would  be  about  20,000  pounds  per 
year,  or  about  1000  tons  per  acre  of  100  trees.  This  is  equivalent  to 
about  9  acre- inches  of  rainfall,  out  of  the  35  inches  commonly  given. 

Since  different  plants  evaporate  very  different  amounts  of 
•water  during  a  given  time,  according  to  their  leaf-surface  and 
the  number  and  size  of  their  stomates,  the  maintenance  of  the 
equilibrium  between  the  soil-supply  and  the  evaporation  of 
the  leaf-surface  requires  correspondingly  varying  moisture- 
conditions  in  the  soil.  Therefore  desert  plants,  with  their 
elaborate  structural  provisions  against  leaf-evaporation,  will 
develop  normally,  and  without  wilting,  under  conditions  which 
in  the  case  of  most  culture  plants  would  result  in  severe  in- 
jury or  death.  Since  diminution  of  leaf-surface  will  in  all 
cases  diminish  evaporation,  the  heroic  measure  of  cutting  back 
the  twigs  and  branches  of  shrubs  and  trees  in  seasons  of  severe 
drought  is  sometimes  resorted  to  in  order  in  save  their  life. 
In  Nature  this  diminution  of  leaf-surface  may  be  observed  in 
many  cases  of  desert  plants,  whose  "  fugacious  "  leaves  are 
developed  during  the  rainy  season,  in  winter  and  early  spring; 
dropping  off  so  soon  as  the  dry  season  begins,  and  leaving  only 
the  green  surface  of  twigs,  stems  or  spines  to  perform  the 
functions  of  the  leaves. 

The  shading  of  the  ground  by  leafy   vegetation   will,   of 


264  SOILS. 

course,  greatly  diminish  and  sometimes  suppress  evaporation 
from  the  soil-surface ;  thus  very  nearly  fulfilling  the  same  con- 
ditions referred  to  above  (chap.  7,  page  in)  in  discussing 
the  effect  of  natural  vegetation  in  rendering  tillage  unneces- 
sary ;  the  beating  of  rains,  and  the  formation  of  surface  crusts, 
being  alike  prevented.  This  fact  is  of  essential  importance  in 
contributing  to  the  welfare  of  crops  sown  broadcast,  where 
subsequent  cultivation  is  impracticable. 

Weeds  Waste  Moisture. — The  injurious  effects  of  weedy 
growth  among  culture  plants  are  in  most  cases  due  quite  as 
much  to  the  appropriation  of  moisture  that  should  have  gone 
to  the  crop,  as  to  the  abstraction  of  plant-food,  to  which  the 
injury  is  generally  attributed.  This  is  much  more  obvious  in 
the  arid  region,  where  during  the  dry  summers  every  pound  of 
moisture  counts,  than  where  summer  rains  obscure  this  in- 
fluence. It  has  led  orchardists  in  California  almost  to  an  ex- 
cess of  clean  culture,  resulting  in  the  burning-out  of  the  humus 
from  the  bare  surface-soil  during  the  long,  hot  summers,  and 
an  injurious  compacting  impossible  to  remedy  by  the  most 
careful  tillage.  It  thus  happens  that  greenmanuring,  the 
natural  remedy  for  this  evil,  cannot  safely  be  done  there  with 
summer  crops,  but  must  be  accomplished  with  winter  crops, 
such  as  can  be  turned  under  before  the  dry  season  begins.  The 
same  objection  holds  against  the  growing  of  summer  crops 
between  the  orchard-rows. 

DISTRIBUTION  OF  MOISTURE  IN  THE  SOIL  AS  AFFECTED  BY 
VEGETATION. 

The  investigations  of  Wollny  and  others  have  long  shown 
quantitatively  what  common  experience  has  taught  the  farmer, 
viz.,  that  a  field  in  crops  or  grass  is  always  drier  within  the  soil- 
mass  penetrated  by  the  roots  than  is  a  cultivated  field  bare  of 
crops,  unless  perhaps  when  heavily  crusted  on  the  surface.  The 
depletion  of  moisture  caused  by  grass  sward  is  the  most  easily 
observed  because  of  the  shallowness  of  the  root-system ;  and 
this  is  one  cause  at  least  why  grass  sward  does  not  occur  natur- 
ally in  the  arid  region,  and  when  planted  cannot  be  maintained 
without  irrigation  repeated  at  short  intervals.  Deeper-rooted 
plants  of  course  deplete  the  soil  at  different  and  varying  levels ; 


THE  WATER  OF  SOILS.  265 

and  where  surface  roots  are  few  or  absent  it  may  readily  hap- 
pen that  the  surface  soil  is  moister  than  the  subsoil. 

This  was  very  strikingly  shown  by  the  investigations  of  Ototzky  in 
the  South-Russian  steppes,  in  comparing  both  the  moisture  contents  and 
the  depth  of  bottom  water  as  between  forest  land  and  the  open  plains. 
On  the  steppe  near  Chipoff,  Government  of  Voronej,  he  found  the 
ground  water  at  from  3  to  5  meters  (10-16  feet)  depth  ;  under  the  forest 
in  the  same  region  and  in  identical  underground  formations,  the  water 
level  stood  at  15  meters.  In  the  Black  Forest  near  Cherson,  the  water 
is  found  at  about  15  feet  beneath  the  surface ;  under  the  steppe  and  in 
cultivated  ground  it  stood  at  10  feet.  At  the  same  time  the  forest  soil 
was  moister  in  the  upper  two  feet  than  the  soil  of  the  steppe,  where 
surface  evaporation  (partly  through  shallow  plant-roots,  partly  direct) 
was  greater  than  under  the  shadow  of  the  forest ;  under  which,  moreover, 
there  were  few  shallow  rooted  plants  to  draw  upon  the  moisture  of  the 
surface  soil. 

The  great  evaporation  from  forests  is  a  matter  demonstrated 
by  actual  measurement ;  hence  it  is  not  surprising  that  certain 
shallow-rooted  trees  should  serve  for  the  reclamation  of  wet 
ground,  as  has  been  demonstrated  on  the  large  scale,  c.  g.,  in 
the  use  of  the  eucalyptus  in  the  Pontine  Marshes  of  Italy,  and 
of  the  maritime  pine  in  the  Landes  of  western  France.  Thus 
the  sanitation  of  swampy  districts  through  tree-planting  has  be- 
come one  of  the  established  measures  in  their  settlement.  But 
this  refers  only  to  the  evaporation  from  the  trees  themselves; 
for  in  the  shade  of  the  forest,  a  free  water-surface  is  found  to 
evaporate  on  the  average  only  one-third  as  much  as  in  open 
ground.  Of  course  there  must  be  a  correspondingly  great 
diffence  in  the  amounts  of  evaporation  from  the  soil-surfaces 
in  the  respective  areas. 

The  great  draft  made  by  the  Eucalyptus  globulus  upon  soil- 
moisture  has  been  also  abundantly  shown  in  California,  where 
on  account  of  its  rapid  growth  this  tree  has  been  largely  used 
for  windbreaks.  Tt  was  found  that  the  trees  deplete  the 
fields  of  moisture  for  from  twenty  to  thirty  feet  on  either  side, 
so  as  to  materially  reduce  crops  within  that  limit.  For  this 
reason  the  pine  and  cypress  has  of  late  found  greater  accept- 
ance for  this  purpose. 


266  SOILS. 

Mulching. — Covering  the  soil  with  straw  or  similar  loose 
materials  to  prevent  waste  of  moisture  is  a  common  garden 
practice  everywhere,  although  not  usually  applicable  on  the 
large  scale.  It  may  readily  however,  be  carried  to  excess,  in 
preventing  not  only  evaporation  but  also  the  warming  of  the 
soil  which  is  so  needful  to  the  thrifty  growth  of  plants.  It 
must  not  therefore  be  done  too  early  in  the  season;  and  after 
cold  rains  it  sometimes  becomes  necessary  to  remove  the  mulch 
in  order  to  allow  the  ground  to  become  properly  warmed. 
Mulching  in  early  spring  is  often  used  to  retard  blooming  of 
trees  where  spring  frosts  are  feared. 

In  the  arid  region,  sanding  of  the  surface  is  sometimes  re- 
sorted to  for  the  prevention  of  the  evaporation  which  brings 
alkali  salts  to  the  surface.  But  the  necessity  of  repeating  this 
dressing  annually  unless  cultivation  can  be  omitted,  restricts 
the  use  of  this  expedient  to  narrow  limits. 

The  sanding  of  the  surface  of  cranberry  plantations  in 
swamps  or  bogs  in  the  northern  parts  of  the  humid  region 
doubtless  owes  its  efficacy  largely,  if  not  chiefly,  to  the  re- 
tention of  moisture,  while  at  the  same  time  it  prevents  the  con- 
solidation of  the  surface,  so  as  to  render  tillage  unnecessary. 


CHAPTER  XIV. 

ABSORPTION  BY  SOILS  OF  SOLIDS  FROM  SOLUTIONS. 
ABSORPTION  OF  GASES.     AIR  OF  THE  SOILS. 

ABSORPTION   OF   SOLIDS   FROM  THEIR  SOLUTIONS. 

JUST  as  solids  have  the  power  of  condensing  gases  upon 
their  surfaces,  to  an  extent  proportional  to  that  surface,  and 
therefore  to  the  state  of  fine  division :  so  fine  powders  have  the 
power  of  withdrawing  from  solutions  solids  held  in  solution, 
to  an  extent  varying  with  the  nature  of  the  substance  dissolved, 
and  the  absorbing  solid.  The  most  commonly-known  mani- 
festation of  this  principle  is  that  sea-water  filtering  through 
the  sands  of  the  shore,  will  at  a  certain  distance  become  sensi- 
bly less  brackish,  and  finally  so  nearly  fresh  as  to  be  capable  of 
domestic  use.1  The  extent  to  which  this  occurs  is  in  a  measure 
proportional  to  the  fineness  of  the  sand,  and  to  the  amount  of 
clay  present  in  it.  This  is  a  clearly  physical  effect,  independent 
of  any  chemical  action  whatever ;  for  it  occurs  equally  with 
quartz  sand,  charcoal,  glass,  limestone,  or  other  rock  powders 
having  no  chemical  effect  upon  the  substance  dissolved  or 
upon  the  liquid  dissolving  it.  Very  large  amounts  of  water  are 
often  required  to  remove  all  the  soluble  matter  thus  "  ad- 
sorbed." 

Decolorizing  Action. — One  of  the  commonest  applications 
of  this  principle  is  the  decolorization  of  colored  solutions  by 
means  of  finely  pulverized  charcoal.  This  property  of  char- 
coal, as  is  well  known,  is  extensively  utilized  in  the  arts,  and 
particularly  in  the  refining  of  sugar;  the  charcoal  used  in  this 
case  being  preferably  bone  charcoal  ("bone  black"),  which 
on  account  of  its  state  (if  extreme  fineness,  and  separation  by 
the  earthy  particles  with  which  it  is  associated,  is  more  effective 
than  any  other  form.  It  is  rendered  still  more  effective,  how- 

1  In  many  cases  this  decrease  of  salinity  is  probably  due  to  a  slow  influx  of  fresh 
water  from  landward  ;  but  very  often  it  cannot  be  thus  explained. 

267 


268  SOILS. 

ever,  by  the  extraction  of  these  earthy  particles  (calcic  carbon- 
ate and  phosphate)  by  means  of  acid;  for  by  removal  of  the 
earthy  particles,  the  surface  of  the  charcoal  is  greatly  increased, 
and  its  decolorizing  as  well  as  its  absorbing  power  increases 
accordingly. 

While  in  one  and  the  same  substance  the  decolorizing  effect 
is  more  or  less  directly  proportional  to  the  fineness  of  the  parti- 
cles, corresponding  to  increased  surface,  it  is  nevertheless  true 
that  in  this  case,  as  in  that  of  the  absorption  of  gases,  there  are 
specific  differences  between  different  powders;  so  that  for  ex- 
ample no  other  substance  can  replace  charcoal  in  the  decoloriz- 
ing effect  which  it  produces  upon  colored  solutions.  It  must 
not,  however,  be  supposed  that  there  is  any  special  reason  why 
coloring  matters,  as  such,  should  be  taken  up  by  preference. 
Coloring  matters  are  of  all  kinds  of  chemical  composition,  and 
have  in  common  only  the  fact  that  a  relatively  small  amount 
produces  a  very  strong  coloring  effect ;  hence  their  name,  and 
hence  also  the  apparently  extraordinarily  strong  effect  pro- 
duced upon  them  by  charcoal. 

This  effect  is  not,  however,  by  any  means  greater  than  it  is 
in  the  case  of  many  other  compounds  which  are  colorless. 

Complex  Action  of  Soils. — The  powdery  ingredients  of 
soils,  of  course,  share  this  power  with  all  other  powders.  In 
the  case  of  soils,  however,  the  action  is  almost  always  much 
more  complex  than  in  that  of  charcoal,  because  solutions  that 
are  passed  through  the  soil  are  apt  to  act  chemically  upon  one 
or  the  other  of  its  ingredients,  usually  resulting  in  a  partial 
exchange  of  ingredients  between  the  soil  and  the  solution ; 
one  or  more  of  the  constituents  of  the  solution  being  retained 
by  the  soil,  while  one  or  more  of  the  (basic)  soil  constituents 
pass  into  the  solution,  in  combination  with  its  acidic  ingredi- 
ents. 

Thus  when  a  very  dilute  (|-  or  i<%)  solution  of  potassic  chlorid  is 
filtered  through  almost  any  soil,  the  first  portions  passing  through  will  be 
practically  free  from  potash,  but  will  contain  the  chlorids  of  calcium 
and  magnesium.  But  as  more  of  the  solution  is  passed  through,  potash 
passes  also  ultimately  without  absorption.  In  addition  to  the  zeolitic 
and  clay  portions  of  the  soil,  the  humus  is  very  effective  in  absorbing 


ABSORPTION  BY  SOILS.  269 

mineral  ingredients  from  solution,  and  retaining  them  in  such  manner 
as  to  be  readily  available  to  plant  growth.     (See  chap.  8,  p.   1 24.) 

In  view  of  the  almost  invariable  conjunction  of  physical  and 
chemical  effects,  it  may  be  fairly  said  that  no  solution,  at  least 
of  mineral  salts,  can  pass  through  the  soil  without  being 
changed  in  its  concentration  and  chemical  composition.  It  is 
sometimes  difficult  to  decide  to  which  of  the  two  classes  of 
effects  the  several  changes  may  be  due. 

Purifying  Action  of  Soils. — The  disinfecting  action  of  dry 
soil,  absorbing  offensive  gases  from  manure  piles  and  from 
earth  closets,  has  already  been  alluded  to.  Similarly  it  is  a 
matter  of  common  experience  that  the  colored  and  otherwise 
offensive  drainage  from  manure  piles,  tanneries,  dyeworks, 
etc.,  is  not  only  deodorized  but  also  decolorized  when  passed 
through  a  sufficiently  thick  layer  of  clay  soil.  The  nitration 
through  fine  sand  by  which  the  drinking  waters  of  cities  are  so 
commonly  purified  before  delivery  to  the  consumer  are  famil- 
iar examples  of  the  same  effects. 

Equally  familiar,  however,  is  the  fact  that  this  power  of 
decolorization  and  retention  of  offensive  compounds  is  limited ; 
that  after  a  while  the  filtering  earth  or  sand  becomes  saturated, 
and  afterwards  the  water  or  drainage  will  pass  through  with- 
out any  sensible  purification. 

It  is  therefore  clear  that  this  purifying  effect  of  earth  can- 
not be  relied  upon  for  the  permanent  protection  of  wells  from 
the  surface-drainage  from  barnyard  or  house  refuse.  Even  if 
fissures  or  layers  of  sand  or  gravel  should  not  intervene  so  as 
to  permit  of  the  direct  communication  of  surface-drainage  with 
wells,  it  is  certain  that  in  the  course  of  a  few  years  at  most, 
the  intervening  earth  will  become  so  far  saturated  with  the 
noxious  ingredients  that  the  latter  will  pass  through  unhin- 
dered, and  may  contaminate  to  a  considerable  extent  the 
domestic  supply  of  drinking  water. 

ll'astc  of  J'Cftiliccrs. — The  same,  of  course,  holds  true  in 
regard  to  manure-water,  or  soluble  fertilizers  of  any  kind  used 
on  the  soil  of  a  field.  The  soil  will  retain  them  to  a  certain 
extent ;  but  beyond  that  limit  any  surplus  added  will  l>e  quickly 
•washed  through  into  the  country  drainage  by  the  rains.  More- 


2/O 


SOILS. 


over,  a  soil  once  so  saturated  will  yield  to  rain-water  filtering 
through  it,  notable  amounts  of  all  the  ingredients  absorbed  in 
it;  and,  at  least  so  far  as  the  physically  condensed  soluble  in- 
gredients are  concerned,  long-continued  leaching  with  pure 
water  will  inevitably  result  in  the  withdrawal  of  additional 
amounts  of  absorbed  ingredients,  apparently  dividing  them- 
selves up  pro  rata  between  the  water  and  the  soil. 

It  is  obviously  of  the  utmost  importance  to  the  farmer  to 
know  to  what  extent  the  soil  will  retain  manurial  ingredients 
against  the  influence  of  leaching  rains;  for  unless  this  is 
taken  into  consideration,  it  may  readily  happen  that  the  fertil- 
izer supplied  before  a  rainy  season  will  be  washed  through  be- 
yond the  reach  of  plant-roots,  and  so  practically  become  a  dead 
loss. 

Absorptive  Power  Varies. — So  far  as  the  mere  physical  ab- 
sorption is  concerned,  it  will  readily  be  understood  that  a 
coarse  sandy  soil  exercises  less  retentive  influence  upon  dis- 
solved substances  than  clay  or  humous  soils.  In  the  humid 
region,  where  sand  is  substantially  nothing  but  granular  silica 
(see  above,  chap.  6,  page  86),  the  same  may  be  measurably 
true  as  regards  the  chemical  absorption  also.  In  the  arid  re- 
gion, on  the  contrary,  a  great  many  sandy  or  silt  soils,  very 
poor  in  clay,  exert  fully  as  much  chemical  absorption  as  clay 
soils,  and  are  no  more  liable  to  the  washing-out  of  soluble 
fertilizers  introduced  than  are  the  latter.  For  the  chemical 
absorption  lies  chiefly  in  the  zeolitic  portion  of  the  soil  (see 
above  chap.  3,  p.  37,  which  in  the  humid  region  accumulates 
in  the  clay,  while  in  the  arid  it  remains  encrusting  the  sand  and 
silt  grains. 

Generalities  regarding  Chemical  Absorption  and  Exchange. 
— In  regard  to  the  leaching-out  and  absorption  or  retention  of 
substances  important  to  agriculture,  the  following  general 
statement  may  be  made  : 

The  substances  most  likely  to  be  leached  out  of  soils  are,  of 
bases :  soda,  magnesia  and  lime ;  of  acidic  constituents :  chlor- 
ine, sulfuric  acid  and  nitric  acid.  Lime  sometimes  passes 
off  with  either  of  the  above  acidic  ingredients,  and  also  in  the 
form  of  carbonate. 

Substances  rather  tenaciously  retained  in  soils  are:  potash 


ABSORPTION  BY  SOILS.  2/1 

and  ammonia  among  the  bases,  and  phosphoric  acid  among-  the 
acids. 

Thus  (as  stated  above)  when  a  weak  (one  or  two  per  cent) 
solution  of  potassic  chlorid  or  sulfate  is  poured  upon  a 
column  of  good  soil  several  inches  thick,  it  will  be  found  that 
the  first  portions  passing  through  are  free  from  potash,  but 
contain  the  chlorids  or  sulfates  of  magnesium  and  calcium. 
If  potassic  nitrate  be  used,  lime  and  magnesia  will  pass  off  as 
nitrates;  while  in  the  case  of  potassic  phosphate,  both  ingredi- 
ents will  be  retained.  A  solution  of  gypsum  (calcic  sulfate) 
will  usually  cause  the  passing-off  of  some  of  the  magnesia,  soda 
and  potash  contained  in  the  soil,  in  the  form  of  sulfates;  but 
the  amount  of  potash  thus  dissolved  soon  diminishes  to  a  mere 
trace.  Solutions  of  potassic  or  ammonic  phosphates  will  be 
absorbed  and  retained  by  the  soil  to  a  very  considerable  extent, 
before  the  soil  becomes  saturated. 

While  it  is  true  that  the  degree  to  which  the  soil  retains 
the  several  ingredients  may  serve  in  a  very  general  way  to 
indicate  their  richness  or  poverty  in  the  same,  the  attempt  to 
make  such  "experiments  serve  to  determine  the  agricultural 
needs  of  soils  has  met  with  but  little  practical  acceptance. 

Drain  H7atcrs. — The  table  on  p.  22,  chapter  2,  illustrates 
forcibly  the  working  of  the  above  principles,  which  are  verified 
by  the  composition  of  drain-waters.  In  all,  the  chief  nutritive 
ingredients  of  plants,  except  nitrogen,  are  present  in  traces 
only;  chlorids,  nitrates  and  sulfates  of  sodium  and  mag- 
nesium form  the  bulk  of  the  permanently  soluble  matter,  with 
usually  a  considerable  proportion  of  calcic  (and  magnesic) 
carbonate,  depending  upon  the  amount  of  the  earth-carbonates 
present  in  the  soil,  as  well  as  upon  that  of  oxidizable  organic 
matter  from  which  carbonic  acid  can  be  formed.  That  calcic 
carbonate  filters  readily  through  the  soil  has  already  been  some- 
what elaborately  discussed  (see  chap.  3.  p.  41);  one  of  the 
results  being  that  the  surface  soil  is  sometimes  almost  com- 
pletely depleted  of  this  important  substance,  while  it  accumu- 
lates at  a  greater  or  less  depth  in  the  subsoil,  or  in  under- 
drains,  as  the  case  may  be. 

Of  the  ingredients  appearing  in  the  above  list,  the  one  of 
greatest  agricultural  importance  is  nitric  acid,  since  chlorine 
and  sulfnric  acid,  as  well  as  soda,  are  required  only  in  very 


272  SOILS. 

small  quantities  by  most  culture  plants;  so  that  they  rarely 
need  to  be  supplied  in  fertilizers.  Nitric  acid,  however,  is  not 
only  one  of  the  most  important  fertilizers,  but  also  the  most 
expensive ;  hence  the  passing-off  of  nitrates  in  drainage-water 
is  of  such  serious  concern  to  the  farmer,  that  the  causes  of  its 
occurrence,  and  the  means  of  preventing  such  loss,  should  be 
fully  understood.  This  subject  will,  however,  be  more  fully 
considered  farther  on. 

The  above  Distinctions  not  Absolute. — It  should,  however, 
be  also  understood  that  while  the  above  statements  hold  good  in 
a  general  way,  yet  the  line  drawn  is  by  no  means  an  absolute 
one.  For  just  as  in  the  case  of  physical  adsorption  the  long 
passing-through  of  distilled  water  will  gradually  abstract  the 
substances  condensed  on  the  surface  of  the  soil-grains,  so  an 
overwhelming  amount  of  a  solution  of  any  one  kind  will  have 
a  tendency  to  substitute  its  own  ingredients  for  those  already 
present  in  the  soil,  removing  the  latter  to  a  greater  or  less 
extent,  even  in  the  case  of  potash  and  phosphoric  acid. 

As  an  example  in  point,  may  be  cited  the  case  of  the  natural  minerals 
Analcite  and  Leucite,  which  Lemberg  was  able  to  reciprocally  trans- 
form from  their  natural  condition  of  soda-  and  potash-alumina  silicates 
merely  by  alternate  treatment  with  solutions  of  potassium  and  sodium 
chlorids  respectively.  (See  chap.  3,  p.  37).  The  same  is  true  in  the 
case  of  the  zeolitic  matter  of  the  soil.  There  is  nevertheless  a  distinct 
preference  in  the  direction  of  the  retention  of  potash  as  against  soda ; 
so  that  in  the  case  of  alkali  soils,  a  large  excess  of  potash  is  found  to 
be  present  in  the  zeolitic  form,  notwithstanding  the  presence  of  some- 
times very  large  amounts  of  the  chlorid,  sulfate  and  carbonate  of  soda. 
This  preferable  retention  of  potash  is,  of  course,  of  material  advantage 
in  the  case  of  the  use  of  soluble  potash-fertilizers,  as  well  as  in  prevent- 
ing the  waste  of  the  potash  of  the  soil  itself. 

ABSORPTION,   OR   CONDENSATION,   OF  GASES   BY   SOILS. 

Like  all  bodies  in  a  state  of  fine  division,  soils  are  capable  of 
absorbing  a  not  inconsiderable  amount  of  various  gases.  It 
may  be  said  that  in  general,  other  things  being  equal,  the 
amount  thus  condensed  on  the  surface  of  the  soil-grains  is  more 
or  less  directly  proportional  to  the  facility  with  which  the  gas 


ABSORPTION  BY  SOILS.  273 

is  condensed  by  either  pressure  or  cooling-.  Hence  the  very 
large  amount  of  water-gas  or  vapor  which  may  be  absorbed  by 
soils,  as  shown  in  a  preceding  chapter.  But  excepting  perhaps 
the  case  of  ammonia,  moist  soils  are  less  absorbent  of  gases 
than  dry  ones. 

Oxygen  and  nitrogen,  the  main  constituents  of  the  atmos- 
phere, being  difficultly  condensable  by  either  pressure  or  cold, 
are  absorbed  by  soils  only  to  a  relatively  small,  yet  by  no 
means  unimportant  extent.  The  condensation  of  oxygen  with- 
in the  soil-mass  is  doubtless  of  considerable  importance  in  the 
processes  of  oxidation,  as  is  shown  by  its  partial  replacement 
by  carbonic  gas  in  the  free  air  of  the  soil  (see  chap.  2,  p.  17). 
The  intensifying  of  oxidizing  action  caused  by  surface  conden- 
sation is  well  illustrated  in  the  case  of  finely  divided  platinum, 
in  which  hydrogen  is  brought  to  rapid  combustion  when  mixed 
with  oxygen ;  as  well  as  by  the  effect  of  bedding  tainted  meat 
in  charcoal  powder,  when  all  odors  of  decay  disappear,  both 
by  absorption  and  oxidation,  ammonia  and  carbonic  gas  alone 
ultimately  escaping  through  the  powder. 

Carbonic  dio.vid  and  ammonia  gases,  both  normal  consti- 
tuents of  the  atmosphere,  and  of  high  importance  to  plant  nu- 
trition, are  more  readily  condensable  than  either  oxygen  or 
nitrogen,  and  consequently  may  be  taken  up  by  the  soil  in 
larger  relative  proportions.  Especially  is  this  the  case  with 
ammonia  gas,  which  is  not  only  readily  condensed  by  pres- 
sure, but  is  also  extremely  soluble  in  water;  so  much  so  that 
it  rushes  into  a  tube  filled  with  this  gas  almost  as  quickly  as 
though  it  were  a  vacuum.  Water  will  absorb  at  the  ordinary 
temperature,  under  normal  pressure,  about  700  times  its  vol- 
ume of  ammonia  gas;  but  inasmuch  as  the  proportion  of  the 
latter  in  the  atmosphere  amounts  to  only  a  few  millionths,  the 
actual  amount  taken  up  can  only  (as  in  the  case  of  all  gases) 
be  proportional  to  its  proportion  (or  "  partial  pressure  ")  mul- 
tiplied into  its  coefficient  of  absorption.  Consequently,  water 
exposed  to  the  ordinary  air  can  absorb  at  best  only  a  small 
fraction  of  a  per  cent  of  ammonia.  Its  presence  in  soils  can 
be  readily  demonstrated  by  passing  through  the  warmed  soil 
a  current  of  purified  air.  which  is  made  to  bubble  through 
Nessler's  reagent  (potassio-mercuric  iodid)  solution. 
18 


274  SOILS. 

Absorption  of  gases  by  dry  soils. — Perfectly  dry  soils  are 
powerful  absorbers  of  ammonia,  and  their  absorption  of  this 
gas,  as  well  as  of  carbonic  gas,  can  readily  be  shown  by  the 
arrangement  shown  on  the  page  opposite. 

The  two  tubes  shown  to  the  left  are  filled  with  carbonic  gas,  those  to 
the  right  with  ammonia  gas.  After  being  immersed  in  a  mercurial 
trough,  there  are  introduced  into  each  tube  through  the  mercury  small 
cylinders  (conveniently  one  cubic  centimeter  in  volume)  consisting  re- 
spectively of  a  very  sandy  soil  or  loose  hardpan,  a  gray  plastic  clay,  a 
gray  clay  soil  or  adobe,  a  very  black  "adobe"  clay,  and  a  highly  ferru- 
ginous and  humous  soil  (from  Hawaii),  which  gives  the  highest  absorp- 
tion of  all ;  next  brown  peat,  and  pine  charcoal.  The  latter,  and  the 
ferruginous  soil,  were  also  exposed  for  the  absorption  of  carbonic  gas. 
All  the  absorbing  cylinders  are  first  heated  for  an  hour  to  i  io°C.  (2  r8°F) 
for  the  purpose  of  expelling  from  them  moisture,  air,  and  other  absorbed 
gases.  They  are  then  quickly  introduced  into  the  tubes  through  the 
mercury  and  allowed  to  absorb  the  gases  enclosed  until  the  mercury 
columns  cease  to  show  any  farther  rise ;  in  which  condition  they  are 
shown  in  the  figure. 

It  will  be  seen  that  this  absorption  is  a  different  one,  not 
only  for  each  of  the  different  substances  used,  but  is  also 
differently  proportioned  for  the  two  gases.  For  it  will  be 
noted  that  while  the  clay  soil  has  absorbed  a  very  much  larger 
amount  of  ammonia  than  the  charcoal,  and  the  sandy  soil  has 
remained  far  behind  both :  yet  the  charcoal  has  absorbed  a 
considerably  larger  proportion  of  carbonic  gas  than  either  the 
clay  or  the  sandy  soil,  proving  that  charcoal  has  a  strong 
specific  absorptive  power  for  carbonic  gas,  independently  of  the 
relative  size  of  clay  and  charcoal  particles  respectively.  The 
sandy  soil  shows,  by  its  low  absorption  even  of  ammonia  gas, 
the  coarseness  of  its  particles  and  the  scarcity  of  clay  in  its 
composition.  The  highest  absorption  of  all  is  shown  by  the 
ferruginous  soil  from  Hawaii,  containing  nearly  40  %  of 
ferric  oxid  together  with  3  1-3%  of  humus.  The  moisture- 
absorption  of  this  soil  at  the  ordinary  temperature  is  19.7  per 
cent.  The  difference  in  the  absorbing  power  of  the  (non- 
humous)  gray  clay  and  gray  adobe  soil  indicates  the  strong  in- 
fluence of  humus  upon  the  absorption;  which  is  still  farther 
emphasized  by  the  difference  between  the  gray  and  black  adobe, 


ABSORPTION  BY  SOILS. 


275 


the  latter  containing  1.2%  of  humus.  As  to  the  peat,  since  its 
weight  was  only  .5  grams  against  an  average  of  2  grams  for 
the  soils  employed,  its  absorptive  power  by  weight  doubtless 
exceeds  all  other  substances. 


Carbonic  gas 
FK;.  51. — Absorption  of  Carbonic  and  Ammonia  Gases  by  different  Soils. 

\Yhile  the  experiment  shown  in  the  figure  serves  as  a  con- 
venient and  striking  demonstration  for  lecture  purposes,  it  is 
of  course  not  adapted  to  a  direct  comparison  of  the  absorbing 
powers  of  the  several  substances,  because  of  different  heights 
of  the  mercurial  columns  counteracting  the  atmospheric  pres- 
sure. For  direct  comparative  measurement  the  tubes  must  be 
sunk  in  mercury  so  as  to  equalize  the  levels  inside  and  outside, 
since  the  corrected  volumes  obtained  by  calculation  would  not 
serve  the  purpose. 

According  to  special  measurements  made  under  normal 
atmospheric  pressure,  the  writer  found  that  a  black  clay  soil 
("adobe")  absorbed  (at  6crF)  over  two  hundred  times  its 
bulk  of  ammonia  gas,  while  under  the  pressure  of  one-fifth  of 
an  atmosphere  (as  shown  in  the  photograph)  the  absorption 
was  one  hundred  and  twenty-three  times  its  bulk.  This  ener- 
getic absorption  of  ammonia  and  related  gases  explains  the 
marked  disinfecting  effects  which  a  covering  of  dry  earth 
exerts  in  the  case  of  cemeteries,  manure  piles,  and  earth  closets. 
But  the  difference  between  the  sandy  soil  and  the  clay  soil  in 


2/6  SOILS. 

the  amount  of  absorption  admonishes  us  that  in  all  these  cases, 
to  secure  disinfection  the  earth  to  be  used  should  contain  as 
much  clay  as  possible,  and  should  not  be  mere  sand,  as  is 
sometimes  the  case.  It  also  shows  that  the  addition  of  charcoal 
to  such  materials  does  not  increase  their  efficacy,  as  has  been 
supposed,  but  that  an  equal  bulk  of  clay  would  be  more  effi- 
cient. 

Of  course,  so  soon  as  the  absorbing  cylinders  used  for  this 
experiment  are  exposed  to  the  atmosphere,  the  principle  above 
stated  in  regard  to  "  partial  pressure  "  asserts  itself.  The  ab- 
sorbed gases  quickly  begin  to  be  given  off,  and  in  some  hours 
the  equilibrium  with  the  ordinary  conditions  of  the  atmos- 
phere is  reestablished.  That  the  strong  absorptive  power  of 
soils  for  ammonia  is  to  some  extent  effective  in  maintaining 
the  supply  of  this  substance  by  absorption  from  the  atmos- 
phere, cannot  be  doubted. 

Boussingault,  and  later  Stenhouse,  determined  the  absorp- 
tive power  of  wood  charcoal  for  ammonia  to  be  90  and  98 
volumes  respectively. 

THE     COMPOSITION     OF     GASES     ABSORBED     FROM     THE    ATMOS- 
PHERE  BY   VARIOUS   SOLIDS. 

In  1864  and  1865  Reichardt  and  Blumtritt  *  investigated 
elaborately  the  composition  of  gases  driven  off  by  heat  from 
various  powders,  including  soils,  exposed  to  the  atmosphere. 
All  the  substances  examined  were  therefore  "  air-dry,"  there- 
fore to  a  certain  extent  moist ;  and  the  presence  of  this  aqueous 
vapor  of  course  modifies  in  a  measure  the  results  that  would 
have  been  obtained  had  the  materials  used  been  exposed  to  dry 
air  only.  They  found  that,  as  had  already  been  stated  by 
previous  observers,  the  presence  of  capillary  water  diminishes 
materially  the  absorption  of  gases,  especially  of  those  not  as 
easily  absorbed  by  water  as  are  carbonic  gas  and  ammonia. 
Contrary  to  what  might  have  been  expected  from  the  more 
ready  condensation  of  oxygen  by  pressure  or  cold,  in  nearly  all 
cases  nitrogen  is  absorbed  to  a  greater  extent  than  oxygen, 
and  sometimes  exclusively  so;  so  that  in  some  cases  the  latter 
was  found  to  be  present  only  in  traces,  as  will  be  perceived 
from  the  subjoined  table : 

1  Journal  fur  praktische  Chemie,  Vol.  98,  p.  167. 


ABSORPTION   BY  SOILS.  277 

COMPOSITION  OF  GASES  ABSORBED  FROM   THE  ATMOSPHERE  BY  VARIOUS  POWDERS. 


Substance. 

100 

Grms 
gave  cc. 
Gas. 

IOO 

Vol's 
gave 
Vol's. 
Gas. 

too  vol's  gas  contained 

M 
o 

2 

d 

be 
>> 

O 

Carbonic 
Dioxid. 

Carbon 
Monoxid. 

Charcoal,  coniferous,  air  dry  

16.21 

100.00 

85.60 
83.60 

44-44 
64.34 
64.70 
67.69 

67-34 
67.40 
70-  17 
59  -S<> 
33-26 
26-29 
82-87 
40.60 
83.09 

IOO.  00 

74-40 
80-81 
77-37 

0.0 
2.  12 
0.0 
4.60 
2.85 
2.04 
0.0 

o.o 

9.09 
4.71 
6.39 
1.43 

3.85 

13.41 

0.00 

16.91 
o.oo 

15.49 
19.19 
15.09 
6.72 

o.o 
9.15 
16.50 
50.96 
24-06 
33-26 
18.61 
30.56 
16.07 
25.12 
34-02 
65-3' 
69.86 
3-72 
59.40 
o.oo 
o.oo 

10.02 
O.OO 

7-54 

o.o 
3-'3 

o.o 

»-7S 
o.o 
'3-7" 

2.  IO 

7-44 

140.1  1 

466.05 
162.58 

59-o 
195.4 

"         Lcmbardy  Poplar  , 

Peat  

13-70 
30.28 
4°  53 
24.12 
26.52 
25-58 
28.62 
25'-59 
375-54 
39  4 
69.02 

10.83 
43.48 

3«.-o8 
65.09 
Si-53 

19.9 
53-6 
48.07 
29.2 
30.05 
39-05 
35-08 
275.0 
3086 
52.4 
82  o 
•3-6 
S^  4 
48.0 

52.0 

"         "         air-dried  

River  Silt,  air-dried  

"     slightly  moistened  

"     slightly  moistened  

Ferric  H  ydrate,  commercial  

o.oo 
o.oo 

freshly  precipitated,  air-dried  

Aluminic  Hydrate,  air-dried  

Prepared  Chalk,  1864-65  
"         1865  

Calcic  Carbonate,  precipitated,  1864-65  
"          1865  66 

Gypsum,  finely  powdered  

17.26 

80.95 

19.05 

o.oo 

Discussion  of  the  Table. — It  will  be  observed  that  in  this  table,  the 
largest  amount  of  total  gas  given  off  by  equal  weights  of  any  one  sub- 
stance was  in  the  case  of  carbonate  of  magnesia  ;  but  it  is  quite  probable 
that  in  part,  at  least,  this  large  amount  of  gas  was  due  to  the  evolution 
of  carbonic  gas  from  the  easily  decomposable  carbonate  ;  the  more  as 
the  analysis  of  the  gases  shows  over  29^  of  carbonic  gas.  But  the 
highest  absorption  by  equal  volumes  of  any  substance  is  shown  by  the 
ferric  hydrate  ;  next  to  this  by  the  light  poplar  charcoal,  and  next  by 
the  carbonate  of  magnesia.  The  high  absorptive  power  here  shown  by 
the  ferric  hydrate  is  of  great  interest  in  connection  with  the  facts  already 
stated  regarding  the  absorption  of  moisture  and  ammonia  by  ferruginous 
soils  (see  page  274,  this  chapter)  ;  and  the  fact  that  the  larger  proportion 
of  the  gas — as  much  as  70%  in  one  case — consisted  of  carbonic  gas,  is 
particularly  interesting  in  the  same  connection.  Both  in  the  amount  of 
gas  contained,  and  in  the  proportion  of  carbonic  gas  therein,  the  ferric 
hydrate  exceeds  even  peat,  the  representative  of  humus  in  soils.  It 
will,  however,  be  noted  that  in  the  garden  soil,  also,  the  proportion  of 
carbonic  gas  is  very  large,  while  that  of  oxygen  is  very  low.  It  is  curious 
to  note  that  in  very  few  cases  the  proportion  of  oxygen  to  nitrogen  is 
the  same  as  in  the  atmosphere  ;  in  most  cases  the  nitrogen  predominates 
considerably  beyond  its  normal  proportion,  and  in  two  cases,  that  of 


278  SOILS. 

charcoal  and  of  calcic  carbonate  (whiting),  the  gas  was  found  to  consist 
of  pure  nitrogen. 

We  are  forced  to  conclude  that  the  substances  here  enumer- 
ated, as  a  rule,  condense  oxygen  in  smaller  proportions  than 
they  do  nitrogen,  or  carbonic  gas.  As  regards  the  carbon 
monoxid  mentioned  in  the  table,  it  is  doubtful  that  it  was  con- 
tained as  such  in  the  substance  originally  examined ;  it  may 
readily  have  been  formed  under  the  influence  of  the  heat  re- 
quired in  expelling  the  gases  from  the  substances  containing 
organic  matter.  Among  the  important  results  shown  in  the 
table,  is  the  comparative  determination  of  the  gases  in  moist, 
and  in  dry  garden  earth,  showing  that  in  the  moist  earth  the 
amount  of  gas  absorbed  ranged  from  less  than  one-half  down 
to  almost  one-fourth  that  absorbed  by  the  dry.  The  import- 
ance of  these  differences  in  the  case  of  the  fallow  can  readily 
be  appreciated. 

The  changes  in  the  absorptive  power  brought  about  by  wetting  and 
drying,  as  shown  in  the  above  table,  are  very  insignificant.  In  the  case 
of  the  charcoal,  soil  and  silt  the  diminution  may  fairly  be  assumed  to 
be  caused  by  the  deposition  of  soluble  salts  on  the  surface,  partly  clog- 
ging the  pores.  In  the  case  of  the  clay  as  well  as  in  that  of  the  river 
silt,  the  inevitable  content  of  organic  matter  in  process  of  decompo- 
sition has  doubtless  influenced  the  result,  as  is  suggested  by  the  increase 
of  carbonic  gas.  That  prepared  chalk  should  in  one  case  contain  ex- 
clusively nitrogen  gas,  in  the  other  case  mixed  gases,  seems  to  indicate 
a  difference  in  the  air  to  which  it  is  exposed,  or  in  the  water  employed 
in  its  preparation  ;  the  latter  case  agreeing  substantially  with  the  results 
obtained  from  the  precipitated  carbonate.  In  both  (as  well  as  in  the 
carbonates  of  barium  and  strontium),  the  absorption  of  carbonic  gas  is 
very  small,  or  nil. 

It  thus  appears  that  for  the  condensation  of  carbonic  dioxid 
gas,  ferric  and  aluminic  hydrates  are  prepotent  among  mineral 
substances;  while  clays,  river  silts  and  soils  may  always  be 
expected  to  contain  relatively  large  proportions  of  this  gas  in 
absorption. 


ABSORPTION  BY  SOILS.  279 

THE  AIR  OF  SOILS. 

The  Empty  Space  in  Soils. — In  dry  soils  the  empty  space, 
usually  amounting  to  from  35  to  50  per  cent  of  its  volume,  is 
filled  with  air;  1  in  moist  or  wet  soils  the  space  unoccupied  by 
water  is  similarly  filled.  Hence  when  soils  are  in  their  best 
condition  for  the  support  of  vegetation  (chap,  n,  p.  202), 
about  one  half  of  their  interstices  is  filled  with  water,  the  other 
half  with  air.  Actual  measurements  of  the  amount  of  air 
contained  in  well-cultivated  garden  soil  have  been  shown  by 
Boussingault  and  Levy  to  range  between  10,000  and  12,000 
cubic  feet  per  acre,  substantially  agreeing,  therefore,  with  the 
above  statement.  In  uncultivated  forest  soil,  on  the  contrary, 
they  found  only  from  somewhat  less  than  4000  to  6000  cubic 
feet  of  air  per  acre.  Extended  observations  since  carried  out 
by  Wollny,  Ebermayer,  and  others  have  in  general  confirmed 
the  earlier  observations,  while  adding  greatly  to  their  signifi- 
cance in  respect  to  their  relations  to  plant  growth,  and  to  the 
process  of  humification  and  soil-formation. 

As  a  matter  of  course,  when  water  evaporates  from  the  soil 
in  drying,  its  place  is  taken  by  air  so  far  as  it  is  not  filled  by 
capillary  water  drawn  from  below. 

Functions  of  Air  in  Soils. — That  roots  require  for  the  per- 
formance of  their  vegetative  functions  the  presence  of  oxygen, 
has  already  been  discussed ;  but  there  can  be  no  question  that 
the  higher  productiveness  of  well-cultivated  soils  is  largely  due 
to  the  greater  and  readier  access  of  air  to  the  roots.  Apart 
from  this  direct  function,  however,  the  presence  of  oxygen  in 
the  soil  serves  other  important  purposes,  and  among  these 
doubtless  the  most  dominant  is  the  promotion  of  the  oxidation 
of  the  organic  matter  of  the  soil  through  the  agency  of  micro- 
organisms; and  more  particularly  that  of  nitrification,  which 
chiefly  governs  the  supply  of  nitrogen  to  non-leguminous 
plants.  In  the  case  of  leguminous  plants,  the  presence  of  air 
as  a  furnisher  of  nitrogen  as  well  as  oxygen  is  absolutely 
essential. 

The  injurious  effects  of  insufficient  aeration  of  the  soil  have 
been  repeatedly  referred  to  already  (pp.  45,  76).  In  water- 
logged soils  reductive  fermentations  are  soon  set  up.  and  the 

1  The  normal  composition  of  atmospheric  air  is  given  on  p.  16,  chap.  2. 


280  SOILS. 

nitrates  of  the  soils  are  reduced  partly  with  the  evolution  ol 
nitrogen  gas,  partly  to  ammonia;  while  their  oxygen  is  con- 
sumed to  supply  the  demands  of  the  roots.  Ferric  oxid  is 
reduced  to  ferrous  carbonate,  sulfates  to  sulfids;  thus  de- 
ranging the  whole  process  of  plant-nutrition  and  absorption  of 
plant-food.  If  continued  for  any  length  of  time  these  condi- 
tions end  in  the  death  of  the  plant.  Too  much  importance  can- 
not therefore  be  attached  to  the  proper  aeration  of  the  soil  and 
subsoil. 

Excessive  Aeration;  Compacting  the  Soil. — On  the  other 
hand,  excessive  aeration  of  the  soil  may  be  injurious  in  caus- 
ing a  serious  waste  of  moisture;  especially  in  arid  climates, 
where  the  hot,  dry  winds  may  readily  destroy  the  germinating 
power  of  the  swollen  seed  when  the  seed-bed  is  too  loose  and 
open,  and  later  may  injure  or  destroy  the  feeding  roots.  The 
abundant  growth  of  grain  often  seen  in  the  tracks  of  a  wagon 
carrying  the  centrifugal  sower,  when  the  stand  in  the  general 
surface  is  very  scanty,  is  usually  due  to  the  consolidation  of  the 
seed-bed,  and  suggests  at  once  the  well-known  efficacy  of  light 
rolling  to  insure  quicker  germination  and  a  better  stand.  Simi- 
larly, the  rolling  of  grain  fields  in  spring  is  often  the  saving 
clause  for  a  crop  in  dry  years.  But  such  needful  consolidation 
must  not,  of  course,  be  carried  to  the  extent  of  creating  a  sur- 
face crust  which  would  subsequently  serve  to  waste  the  subsoil 
moisture.  Hence,  the  soil-surface  should  be  rather  dry  when 
rolling  is  resorted  to. 

The  pressing  of  the  earth  around  transplanted  plants,  simi- 
larly, is  a  needful  precaution,  not  only  with  respect  to  the  dry- 
ing-out of  the  soil,  but  also  to  insure  close  contact  between  the 
roots  and  the  soil. 

The  Composition  of  the  Free  Air  of  the  Soil  usually  differs 
from  the  air  above,  in  that  besides  being  saturated  with  mois- 
ture, its  nitrogen-content  is  slightly  increased  (by  one-half  to 
over  one  per  cent)  ;  the  oxygen-content  on  the  other  hand,  is 
diminished,  being  in  part  (sometimes  nearly  to  the  extent  of 
one-half  of  its  volume)  replaced  by  carbonic  gas,  de- 
rived partly  from  its  secretion  by  the  roots,  partly  from  the 
oxidation  of  organic  substances.  It  naturally  follows  that  the 
richer  the  soil  in  the  latter,  the  more  carbonic  gas  will  be 
formed  under  favoring  conditions ;  so  that  in  freshly-manured 


ABSORPTION  BY  SOILS.  28l 

land  the  amount  of  oxygen  transformed  into  carbonic  gas  will 
be  greatest,  while  in  the  surface-soil  of  ordinary  fields,  car- 
bonic gas  rarely  reaches  to  as  much  as  one  per  cent.  In  all 
cases,  however,  the  content  of  carbonic  gas  in  the  air  of  the 
soil  is  materially  higher  than  that  of  the  air  above  it,  and  thus 
serves  to  intensify  greatly  the  solvent  and  disintegrating  effect 
of  the  soil  water  upon  the  soil  materials  (see  chap.  2,  p.  17). 
The  soil-mass  itself,  however,  retains  carbonic  dioxid  with  con- 
siderable tenacity,  so  that  it  is  not  possible  to  wash  it  out  com- 
pletely by  filtering  water  through  it.  When  water  containing 
carbonic  gas  in  solution  is  filtered  through  the  soil,  the  gas  is 
sometimes  completely  absorbed,  the  water  passing  off  free 
from  gas. 

The  presence  of  free  carbonic  gas  in  soils  is  readily  demon- 
strated by  passing  through  the  warmed  soil  a  current  of  air, 
which  is  then  made  to  bubble  through  lime  water ;  a  clouding 
of  the  latter,  and  the  ultimate  formation  of  a  precipitate  of 
calcic  carbonate,  proves  the  presence  of  the  gas,  and  may  also 
serve  to  measure  its  amount. 

From  the  fact  that  the  free  air  in  normal  soils  may  contain 
as  much  as  one-fortieth  of  its  bulk  of  carbonic  gas,  besides 
what  may  be  contained  in  the  condensed  form,  we  may  con- 
clude that  this  gas  is  formed  within  them  with  considerable 
rapidity;  for  otherwise,  in  view  of  the  free  communication  and 
diffusion  with  the  outer  air,  such  large  amounts  could  not  be 
maintained  in  the  surface-soil.  Doubtless  a  considerable  pro- 
portion of  the  carbonic  gas  normally  contained  in  the  atmos- 
phere is  thus  supplied  from  within  the  soil  itself. 

Relation  of  Carbonic  Gas  to  Bacterial  and  Fungous  Activity. 
—It  has  been  fully  demonstrated  by  the  researches  of  Koch, 
Miqucl,  Adametz,  Fuelles,  \Yollny  and  others,  that  the  forma- 
tion of  carbonic  gas  in  the  soil  is  not  a  purely  chemical  oxida- 
tion process,  but  is  essentially  dependent  upon  the  presence  and 
life-activity  of  numerous  kinds  of  organisms,  bacterial  as  well 
as  fungous.  The  crucial  proof  of  this  fact  is  that  the  presence 
of  any  antiseptic  diminishes,  and  if  exceeding  certain  propor- 
tions completely  suppresses,  the  formation  of  carbonic  gas; 
while  on  the  other  hand  all  conditions  known  to  l^e  favorable 
to  the  life  of  such  organisms,  viz..  the  proper  conditions  of  tem- 
perature and  moisture  (varying  with  different  kinds),  increase 


282  SOILS. 

the  formation  of  the  gas.  Such  formation  is  of  course,  how- 
ever, conditioned  upon  the  presence  of  oxygen.  In  the  case  of 
most  bacteria,  there  is  a  certain  limit  beyond  which  the  pres- 
ence of  their  own  product  exerts  an  injurious  or  repressive 
effect  upon  their  activity ;  so  that  if  the  gas  accumulates  beyond 
that  limit,  the  rate  of  its  formation  decreases  despite  of  other- 
wise favorable  conditions. 

It  follows  that  the  best  life-conditions  of  these  organisms 
(even  when  anerobic)  cannot  be  fulfilled  below  a  certain 
limited  depth  in  the  soil;  and  all  observations  show  that  their 
number  decreases  very  rapidly  with  increasing  depth  (see 
chap.  9,  p.  142),  varying  with  the  perviousness  of  the  soil, 
but  rarely  exceeding  four  or  five  feet  in  the  humid  regions; 
though  doubtless  found  at  greater  depths  in  the  arid  climates. 
It  is  also  obvious  that  the  use  of  any  antiseptic  or  poisonous 
materials  on  the  field  or  in  the  manure  pile  will  tend  to  disturb 
and  restrain  the  useful  activity  of  these  organisms. 

Putrefactive  Processes. — Carbonic  gas  is  formed  also,  but  to 
a  much  more  limited  extent,  in  putrefactive  processes,  occur- 
ring in  the  absence,  or  with  only  limited  access,  of  air  or 
oxygen.  These  processes  likewise  are  conditioned  upon  the 
presence  or  activity  of  (largely  anerobic)  bacteria;  but  they 
should  not  occur  in  normally  constituted,  and  especially  in  tilled 
soils,  being  as  a  rule  inimical  to  the  growth  of  cultivated 
plants  (see  chap.  9,  p.  145). 


CHAPTER  XV. 

THE  COLORS  OF  SOILS. 

THE  natural  coloration  of  soils  forms  a  prominent  part  of 
the  characters  upon  which  farmers  are  wont  to  base  their  judg- 
ment of  land  quality;  hence  the  origin  and  value  of  soil-colors 
deserve  consideration. 

Black  Soils. — From  the  oldest  times  down  to  the  present  a 
"  rich,  black  soil  "  has  commanded  attention  and  approval. 
The  black  and  brown-black  colors  being  almost  invariably  due 
to  the  presence  of  much  humus  (very  rarely  to  an  admixture 
of  carbon  (graphite),  of  magnetic  oxid  of  iron,  or  sesquioxid 
of  manganese),  it  is  obvious  that  the  farmers'  judgment  coin- 
cides with  a  high  estimate  of  the  agricultural  value  of  humus. 
A  discussion  of  this  point  will  be  found  in  another  place;  but 
the  popular  judgment  is  based  quite  as  much  upon  the  experi- 
ence had  in  the  advantages  that  usually  accompany  the  pres- 
ence of  humus.  It  largely  characterizes  low  grounds,  and 
therefore  alluvial  lands,  whose  richness  is  due  to  far  more  gen- 
eral causes.  But  the  shade  of  the  blackness  seen  in  the  soil 
deserves  and  usually  receives  close  consideration.  If  tending 
toward  brown,  acid  humus  or  "  sour  "  land  is  indicated ;  unless 
indeed  the  surface  soil  should  be  bodily  derived  from  decayed 
wood,  as  in  the  primeval  forests.  Forest  soils  in  general  are 
usually  dark-tinted  for  some  inches  near  the  surface,  owing 
to  the  presence  of  leaf  mold,  and  mostly  have  an  acid  reaction. 

But  the  black  tint  is  equally  welcome  to  the  land-seeker  when 
seen  outside  of  alluvial  and  forest  areas.  Belts  of  "black 
lands"  appear  on  hillsides  and  plateaus;  and  these  lands, 
though  clearly  not  alluvial,  are  also  found  to  be  preeminently 
productive;  witness  the  upland  prairies  of  the  western  and 
southern  United  States.  These  black  soils  are  always  charac- 
terized by  the  presence  of  a  full  supply  of  lime  in  the  form  of 
carbonate,  under  the  influence  of  which  the  most  deeply  black- 
humus  is  formed.  In  other  words,  the  jet  black  tint  is  indica- 

28} 


284  SOILS- 

tive  of  calcareous  lands ;  and  these,  as  will  be  more  fully  shown 
below,  are  almost  always  highly  productive. 

From  both  points  of  view,  then,  the  favorable  judgment 
passed  upon  black  soils  by  practical  men  is  justified. 

But  it  is  not  necessarily  true  that  soils  showing  no  obvious 
black  tint  are  poor  in  humus;  for  in  strongly  ferruginous  or 
"  red  "  soils  its  tint  is  frequently  wholly  obscured,  though 
when  still  visible  it  gives  rise  to  the  laudatory  name  of  "  ma- 
hogany land,"  which  every  farmer  considers  a  prize. 

Of  course  then  it  would  be  wholly  incorrect  to  judge  of  the 
agricultural  value  of  land  from  its  humus-content  alone;  for 
its  color  may  be  entirely  imperceptible  and  yet  its  amount  and 
nitrogen  content  be  fully  adequate  to  the  requirements  of 
thrifty  vegetation.  Gray  and  even  whitish  soils  very  fre- 
quently fall  within  this  category  in  the  arid  region. 

The  black  tint  is  also  favorable  to  the  absorption  of  the 
sun's  heat,  and  is  therefore  conducive  to  earlier  maturity  than 
is  to  be  looked  for  in  light-tinted  lands  similarly  located. 

Wollny  (Forsch.  Agr.  Phys.  Vol.  12,  1889,  p.  385),  dis- 
cusses the  influence  of  color  on  soils  in  relation  to  moisture  and 
content  of  carbonic  acid.  The  results  show  in  general  simply 
the  effects  due  to  increase  of  temperature  when  the  soils  are 
either  darker-colored  throughout,  or  made  so  superficially. 

"  Red  "  Soils. — Next  to  a  black  soil,  a  "  red  "  one  will  usu- 
ally command  the  instinctive  approval  of  farmers.  The  cause 
of  this  preference  is  not  as  obvious  as  in  the  case  of  the  black 
tints;  but  the  general  consensus  of  opinion  requires  an  ex- 
amination of  its  claims.  It  is  of  course  easy  enough  to  adduce 
examples  of  very  poor  "  red  "  soils,  derived  from  ferruginous 
sandstones  that  supply  little  else  than  quartz  and  ferric  hy- 
drate ;  the  Cotton  States  supply  cogent  examples  in  point,  as 
do  also  the  lower  Foothills  of  the  Sierra  Nevada  of  Cali- 
fornia. It  is  not,  therefore,  the  iron  rust  or  ferric  hydrate  that 
renders  the  land  productive;  but  its  presence  is  a  sign  of  some 
favorable  conditions.  First  among  these  is,  that  ferric  hydrate 
cannot  continue  to  exist  in  badly  drained  soils;  a  "  red  "  soil 
is  therefore  a  well-drained  one,  and  this  is  probably  one  of  the 
chief  causes  of  the  popular  preference.  The  "  white  land  " 
sometimes  seem  in  tracts  otherwise  colored  with  iron,  is  dis- 
tinctly inferior  in  production  to  the  red  lands ;  and  examination 


THE  COLORS  OF    SOILS.  285 

will  generally  show  that  from  some  cause,  such  white  lands 
have  been  subjected  to  the  watery  maceration  which  proves  so 
injurious  (see  chap.  3,  p.  46,  chap.  12,  p.  231). 

That  finely-diffused  ferric  hydrate  has  a  very  high  power  of 
absorbing  moisture  as  well  as  other  gases  of  the  atmosphere, 
has  been  shown  in  the  preceding  chapter;  it  stands  in  this  re- 
spect next  to  humus  itself,  and  hence  highly  ferruginous  soils 
need  not  contain  as  much  humus  as  "  white  "  soils  from  this 
point  of  view.  Like  humus,  also,  it  renders  heavy  clay  soils 
more  easily  tillable. 

Origin  of  Red  Tints. — Where  crystalline  rocks  prevail,  the 
red  tint  usually  indicates  the  derivation  from  the  weathering  of 
hornblende ;  implying  also,  outside  of  the  tropics,  the  presence 
of  sufficient  lime  in  the  land.  Such  lands  are  naturally  pre- 
ferred to  those  of  lighter  tints  derived  from  purely  feldspathic 
rocks  (see  chap.  3,  p.  32),  although  they  may  be  poorer  in 
potash  than  the  latter. 

But  the  red  tint  has  also  its  intrinsic  advantages  in  the  more 
ready  absorption  of  the  sun's  heat  by  the  colored  than  by  a 
white  surface.  This  is  probably  the  chief  cause  of  the  higher 
quality  of  wines  grown  on  red  hillsides  in  the  middle  and 
northern  vine  districts  of  Europe,  where  everything  that  aids 
earlier  maturity  is  of  the  greatest  importance.  The  function 
of  ferric  oxid  as  a  carrier  of  oxygen  (chap.  4  p.  45)  prob- 
ably also  aids  nitrification. 

"  Yellow "  lands  owe  their  tint,  of  course,  to  smaller 
amounts  of  ferric  hydrate,  but  share  more  or  less  in  the  ad- 
vantages of  the  "  red." 

White  soils,  or  more  properly  those  having  very  light  gray 
tints,  are  not  usually  looked  upon  with  favor,  especially  in  the 
humid  region.  The  causes  of  the  unfavorable  judgment  cur- 
rent among  fanners  in  respect  to  white  soils  has  already  been 
partially  explained  in  the  discussion  of  the  black  and  red  tints. 
The  light  color  means  the  scarcity  or  absence  of  both  humus 
and  ferric  hydrate,  and  usually  implies  that  the  soil  has  been 
subject  to  reductive  maceration  through  the  influence  of  stag- 
nant water;  reducing  the  ferric  hydrate  to  ferrous  salts,  oxidiz- 
ing away  the  humus,  and  accumulating  in  the  form  of  inert 
concretions  most  or  all  of  the  lime,  iron  and  phosphoric  acid  of 
the  soil  mass  (see  chap.  3,  p.  46,  chap.  10,  p.  184).  The 


286  SOILS. 

term  "  crawfishy,"  so  commonly  applied  to  white  soils  in  the 
eastern  United  States,  expresses  well  the  usual  condition  of 
the  white  soils  of  that  region;  which  are  very  commonly  in- 
habited by  crayfish,  whose  holes  reach  water  a  few  feet  below 
ground,  and  are  surrounded  on  the  outside  by  piles  of  white 
subsoil  mixed  with  "  black  gravel  "  or  concretions  of  bog  iron 
ore.  It  is  needless  to  say  why  such  lands  cannot  command  the 
favorable  consideration  of  the  farmer;  they  cannot  as  a  rule 
be  cultivated  without  previous  drainage,  and  even  after  that 
will  usually  prove  unthrifty,  "  raw,"  and  in  immediate  need  of 
fertilization  by  greenmanuring,  and  the  use  of  phosphates. 

In  the  arid  region,  lands  of  this  character  are  of  rare  occur- 
rence, while  (as  has  been  explained  above,  chap.  8,  p.  135), 
the  light  gray  or  "  white  "  tints  are  there  a  very  common  char- 
acteristic of  even  the  very  best  soils.  It  is  true  that  they  are 
poor  in  humus  and  in  finely  diffused  ferric  hydrate;  but  their 
"  light  "  texture  renders  the  presence  of  humus  for  this  pur- 
pose less  needful,  and  as  stated  elsewhere  (see  chap.  8,  p. 
135),  the  high  nitrogen-content  of  arid  humus  renders  a 
smaller  supply  adequate  for  vegetative  purposes.  As  to  iron, 
its  presence  being  more  important  as  a  sign  of  good  drainage 
and  aeration  than  directly,  its  absence  from  soils  of  great 
depth  and  loose  texture  is  of  no  consequence ;  especially  when 
the  heat-absorption  which  it  favors  is  not  only  not  needed,  but 
is  usually  already  in  undesirable  excess  during  the  hot  sum- 
mers. 

White  Alkali  Spots. — In  the  valleys  of  the  arid  region,  how- 
ever, very  white  spots  commonly  indicate  the  prevalence  of 
alkali  salts,  and  to  that  extent  are  an  unfavorable  indication ; 
especially  when  coupled  with  the  occurrence  of  black  rings  or 
spots,  which  indicate  the  presence  of  black  alkali  or  carbonate 
of  soda  (see  chap.  22). 


CHAPTER  XVI. 

CLIMATE. 

Heat  and  Moisture  are  the  main  governing  conditions  of 
plant  growth.  In  a  preceding  chapter  the  relations  of  soils  and 
plant  growth  to  water  have  been  considered ;  in  the  present  one 
the  relations  of  both  moisture  and  heat  to  soils  and  plants  will 
be  discussed ;  and  to  do  this  intelligibly  to  those  not  making 
a  specialty  of  such  studies,  it  becomes  necessary  to  introduce, 
first,  a  summary  consideration  of  the  subject  of  climate. 

Climatic  conditions  control,  and  to  a  great  extent  determine, 
the  industrial  pursuits  of  every  country ;  all  the  more  so  as  the 
rapid  communication  and  transportation  by  means  of  modern 
appliances  now  brings  every  part  of  the  globe  in  competition 
with  every  other.  The  question  is  not  now  what  it  may  be 
intrinsically  possible  to  do  under  certain  climatic  and  geo- 
graphical conditions,  but  whether  these  things  can  be  done  with 
a  reasonable  prospect  of  profit  and  commercial  success,  in 
competition  with  other  countries  offering  more  or  less  of  simi- 
lar possibilities.  While  it  is  true  that  the  cost  of  labor  fre- 
quently enters  most  heavily  into  such  problems,  yet  favorable 
or  unfavorable  climatic  or  soil-conditions  may  in  many  cases 
turn  the  scale.  Thus  the  high  price  of  labor  and  fuel  on  the 
Pacific  coast  of  the  United  States  would  at  first  blush  seem 
to  render  competition  with  Europe  and  the  East  in  the  pro- 
duction of  beet  sugar  commercially  impossible;  yet  exception- 
ally favorable  climatic  and  soil-conditions  concur  to  turn  the 
scale  in  favor  of  California  at  least,  so  as  to  have  placed  that 
state  at  the  head  of  the  sugar-producing1  states  of  the  Union. 
A  general  understanding  of  the  climatic  conditions  which  con- 
cern the  United  States  more  or  less  directly,  is  therefore  need- 
ful to  an  appreciation  of  their  agricultural  possibilities. 

Climatic  Conditions. — The  factors  usually  mentioned  as 
constituting  climate  are  temperature,  rainfall  and  winds. 
Since  the  latter  two  factors,  however,  are  themselves  merely 

287 


288  SOILS. 

the  result  of  heat  conditions,  it  is  proper  to  discuss  from  the 
outset  the  origin  and  mode  of  action  of  heat. 

TEMPERATURE. 

The  temperature  of  stellar  space  outside  of  the  atmosphere 
is  known  to  be  very  low.  The  increasing  cold  as  we  ascend  to 
greater  heights,  is  a  fact  familiar  to  all.  Langley  has  calcu- 
lated upon  the  basis  of  observations  made  at  the  summit  and 
foot  of  Mount  Whitney  in  California,  that  the  temperature  of 
space  lies  near  200°  Cent.  (360°  F.)  below  the  freezing  point 
of  water;  and  this  would  be  the  temperature  near  the  Earth's 
surface,  were  it  not  for  the  surrounding  atmosphere.  The  lat- 
ter absorbs  but  a  small  amount  of  the  sun's  direct  heat  rays 
(which  are  of  high  intensity),  as  they  penetrate  it  to  the 
Earth's  surface.  But  as  the  earth's  surface  is  warmed,  the 
heat  rays  of  low  intensity  which  it  emits  cannot  pass  back 
through  the  atmosphere  to  the  sun  or  to  outer  space ;  they  are 
"  trapped,"  as  it  were,  by  the  dense  air  resting  near  the  earth's 
surface,  which  is  then  warmed  partly  by  the  radiation  from, 
partly  by  direct  contact  with,  the  soil.  It  is  to  the  existence  of 
our  atmosphere,  then,  that  the  possibility  of  our  animal  and 
vegetable  life  in  their  present  form  is  due;  and  a  decrease  of 
the  trapping  effect  on  the  sun's  heat  rays  makes  itself  quickly 
felt  when  ascending,  either  in  balloons  or  on  high  mountains. 
Moreover,  it  is  well  known  to  mountain  climbers  that  at  great 
elevations  the  sun's  heat  is  extremely  intense  at  noon ;  even 
though  the  temperature  may  fall  to  the  freezing  point  at  night, 
owing  to  the  failure  of  the  thin  air  to  prevent  the  radiation 
back  into  space  of  the  heat  absorbed  during  the  day.  On  the 
high  plateaus  of  the  Andes  and  of  Asia,  therefore,  very  ex- 
treme climates  prevail,  on  account  of  the  great  range  of  tem- 
perature between  day  and  night. 

Ascertainment  and  Presentation  of  Temperature-Conditions. 
— The  proper  understanding  of  the  temperature  conditions  of 
any  locality  or  region  is  by  no  means  a  simple  matter.  Shall 
we  study  the  daily,  monthly,  or  annual  changes  of  temperature, 
or  the  means  deduced  from  either  or  all  of  them,  in  order  to 
gain  a  clear  insight  into  the  climatic  conditions  that  control 
crop  production  and  health  conditions? 


CLIMATE. 

The  Annual  Mean  Temperature  not  a  Good  Criterion. — 
Since  one  and  the  same  figure  may  result  equally  from  the 
averaging  of  two  widely  divergent  data,  and  from  such  as  are 
close  together,  it  is  clear  that  the  mean  annual  temperature 
cannot  be  a  proper  criterion  of  the  agricultural  adaptations  of 
a  country.  Thus  an  average  temperature  of  60°  F.  might  re- 
sult, equally,  from  the  averaging  of  65  and  55  degrees,  or  from 
taking  the  mean  of  15  and  105  degrees;  yet  the  respective  cul- 
tural adaptations  would  be  widely  different. 

Extremes  of  Temperature  arc  Most  Important. — It  is,  on 
the  contrary,  rather  the  extremes  of  temperature,  more  par- 
ticularly of  cold,  but  frequently  also  of  heat,  together  with  the 
total  amount  of  heat  available  during  the  growing  season, 
that  determines  such  adaptation  so  far  as  temperature  is  con- 
cerned ;  for  no  culture  plant  can  be  successfully  grown  where 
the  temperature  during  winter  even  occasionally  falls  for  more 
than  a  few  hours  below  the  point  which  it  can  resist;  and  for 
each  plant  there  is  a  certain  aggregate  requirement  of  heat  to 
carry  it  from  germination  to  fruiting.  Even  different  varie- 
ties of  one  and  the  same  plant  differ  materially  in  the  latter 
respect,  so  that  it  is  very  important  that  in  the  selection  of 
varieties  to  be  grown,  this  factor  should  be  taken  into  con- 
sideration. It  cannot  be  too  strongly  urged  that  the  compari- 
son of  annual  means  of  temperature,  so  commonly  made  by 
promoters  of  colonization  schemes,  must  not  be  taken  as  a 
guide  either  in  the  estimate  of  cultures  in  which  the  immi- 
grant may  desire  to  engage,  or  by  those  in  search  of  a  climate 
adapted  to  their  health-conditions. 

Seasonal  and  Monthly  Means. — The  statement  of  the  mean 
temperatures  of  the  conventional  four  seasons — spring,  sum- 
mer, autumn  and  winter — afford  a  much  clearer  conception  of 
climatic  adaptations;  provided  always  that  the  extreme  tem- 
peratures be  considered  at  the  same  time.  \Yith  the  same  un- 
derstanding, the  monthly  means  are  still  more  instructive;  but 
here  again,  it  is  most  essential  that  the  distribution  and  amount 
of  rainfall  in  each  be  regarded  at  the  same  time,  since  the  most 
desirable  temperature  is  of  no  avail  without  the  moisture  re- 
quired for  vegetation. 

In  some  cases,  c.  £..  that  of  California,  it  becomes  neces- 
sary for  practical  purposes  to  regard  the  "  season,"  and  not 
19 


290  SOILS. 

the  calendar  year,  as  the  unit  or  reference  for  crop  production. 
There  the  crops  depend  upon  what  rainfall  may  occur  from 
October  to  May,  there  being  no  summer  rains  of  agricultural 
significance,  and  outside  of  irrigated  lands,  almost  all  vegeta- 
tion save  that  of  trees  being  in  abeyance.  In  India,  there  are 
two  distinct  growing  seasons  ("  kharif  "  and  "  rabi  "),  corre- 
sponding to  the  two  "  monsoon  "  seasons;  and  no  matter  how 
much  rain  may  fall  during  one,  almost  total  failure  may  occur 
in  other  tropical  and  arid  sections  of  that  country. 

The  Daily  Variations  are  of  interest  chiefly  with  respect  to 
health  conditions,  since  most  plants  are  more  adaptable  in  this 
respect  than  the  average  man. 

RAINFALL. 

Distribution  Most  Important. — The  summary  statements  of 
the  annual  rainfall  are  almost  equally  as  deceptive  as  are  those 
of  annual  mean  temperature,  since  quite  as  much  depends  on 
the  manner  in  which  it  is  distributed  through  the  year,  as  upon 
its  absolute  amount ;  and  also  upon  the  manner  of  its  fall. 
Thus  Central  Montana  has  the  same  aggregate  annual  rainfall 
as  the  country  surrounding  the  Bay  of  San  Francisco,  viz. 
about  24  inches ;  but  while  in  the  Franciscan  climate  this 
amount  of  rain  falls  during  one-half  of  the  year,  and  that  the 
growing  season,  enabling  crops  to  be  grown  without  irrigation, 
in  Montana  the  rainfall  is  distributed  over  the  entire  season, 
so  that  irrigation  is  absolutely  essential  for  the  successful  pro- 
duction of  crops.  This  so  much  the  more  as,  while  the  winter 
snowfall  is  very  light,  the  rains  of  summer  are  largely  torren- 
tial, running  off  the  surface  in  muddy  floods  and  giving  little 
time  for  absorption  into  the  soil.  Farther  west,  in  Washing- 
ton, where  grain  crops  are  largely  grown  without  irrigation, 
the  sowing  of  winter  grain  is  impracticable  because  the  dry 
summer  is  immediately  followed  by  the  very  light  snowfall  of 
winter,  which  falls  on  dry  ground.  Fall-sown  grain  would 
thus  simply  lie  dormant  in  the  ground  through  the  winter, 
with  great  liability  to  injury  from  stress  of  weather  in  early 
spring,  apart  from  the  depredations  of  birds  and  rodents. 
Hence  grain  is  always  sown  there  in  spring  only. 

These  examples  may  suffice  to  show  that  summary  state- 


CLIMATE. 


291 


ments  of  either  temperature  or  rainfall  by  yearly  means  are 
of  little  practical  interest  to  the  farmer.  \Yhat  he  needs  to 
know  is  whether  or  not  sufficient  rains  to  mature  a  full  crop 
are  likely  to  fall  during  the  time  that  the  growing  temperature 
prevails ;  and  what  are  the  minima  and  maxima  of  temperature 
— heat  and  cold — that  his  crops  will  be  called  upon  to  endure. 

WINDS. 

The  third  climatic  factor  mentioned,  the  winds,  though 
proverbial  for  their  unreliability  and  inconstancy,  are  not  only 
very  incisive  in  their  action,  but  also  to  a  considerable 
extent  of  very  definite  local  or  regional  occurrence  and  signifi- 
cance. Moreover,  their  occurrence,  direction,  temperature  and 
moisture-condition  can,  in  regions  whose  climatology  has  been 
reasonably  well  studied,  be  foretold  with  sufficient  accuracy 
to  be  of  great  use  to  the  farmer. 

Heat  the  Cause  of  IVinds. — As  already  stated,  the  primary 
cause  of  all  winds  is  heat,  substantially  on  the  principle  accord- 
ing to  which  draught  is  created  in  our  domestic  fires.  The 
hot  air  rising  creates  an  indraught  from  all  directions,  especi- 
ally from  that  which  it  can  most  readily  come;  viz.,  from 
the  ocean,1  or  from  level  lands,  rather  than  across  mountain 
chains.  Hence  the  sea-breeze  in  the  after  part  of  the  day,  when 
the  land  has  become  heated;  while  the  sea.  requiring  a  much 
larger  amount  of  heat  to  change  its  temperature  to  a  similar 
extent,  remains  relatively  cool.  Rut  at  night  the  earth  cools 
more  rapidly  than  the  sea,  by  radiation;  hence  toward  evening 

1  A  striking  case  in  point  is  the  regular  wind  which  in  summer  blows  through 
the  "  Golden  Gate,"  a  gap  in  the  Coast  Range  connecting  the  Pacific  Ocean 
directly  with  the  great  interior  valley  of  California,  along  the  hays  of  San 
Francisco,  San  Pablo,  and  Suisun.  The  great  interior  valley  and  adjacent  moun- 
tain slopes  becoming  intensely  heated  during  the  rainless  summer,  the  ascending 
air  is  replaced  by  a  steady  indraught  from  the  sea,  which  is  bordered  by  a  belt  of 
cold  water  causing  fogs  along  the  coast.  The  fogs  are  quickly  dispelled  on  reach- 
ing the  edge  of  the  valley  near  the  middle  of  its  length  ;  whence  steady  bree/es 
blow  northward  and  southward,  up  the  valleys  of  the  Sacramento  and  San 
Joaquin  respectively.  These  winds,  popularly  often, but  erroneously, called  trade- 
winds,  are  really  "  monsoons  "  similar  in  their  origin  to  those  of  India,  which, 
when  coming  from  the  sea  cause  rains,  but  when  from  the  heated  land  itself  are 
hot  and  dry;  as  in  the  case  of  the  sirocco  of  Italy  and  Xorth  Africa,  the  terral  of 
Spain  and  the  northers  of  California. 


292 


SOILS. 


the  sea-breeze  dies  down,  and  toward  and  after  sunset  the 
land-breeze  takes  its  place. 

The  principle  of  this  local  change  of  winds,  together  with 
the  rotation  of  the  earth,  the  absorption  of  moisture  by  air, 
and  the  fact  that  the  latter  becomes  cooler  when  it  expands 
on  rising  and  warmer  when  it  is  compressed  by  descending, 
serves  to  explain  all  the  major  phenomena  usually  observed 
in  connection  with  winds.  The  air  of  the  equatorial  belt, 
heated  throughout  the  year,  necessarily  rises  and  creates  an 
indraught  from  both  north  and  south;  but  since  the  air  thus 
flowing  in  has  a  lower  rotary  velocity  than  the  earth's  surface 
at  the  Equator,  it  lags  behind  and  so  gives  rise  to  northeast 
and  southeast  winds,  respectively,  between  the  two  tropics  and 
the  equatorial  belt.  These  regular  winds,  from  the  aid  they 
give  to  commerce  in  passing  from  continent  to  continent,  are 
known  as  the  trade  "winds.  On  the  other  hand,  the  air  that 
has  risen  from  the  hot  equatorial  belt,  cooling  by  expansion 
as  it  rises  and  flowing  northward  and  southward  from  the 
Equator,  on  descending  as  it  mainly  does  into  the  temperate 
zones,  has  a  higher  rotary  velocity  than  the  land-surface  and 
so  tends  to  give  rise  to  southwest  and  northwest  winds  in  the 
northern  and  southern  hemispheres  respectively.  At  sea,  on 
coasts  and  in  level  inland  regions  to  windward  of  mountain 
chains,  such  winds  are  often  quite  regular  during  a  portion  of 
the  year. 

Cyclones. — But  local  disturbances  arising  from  heated  land 
areas  or  mountain  slopes,  as  well  as  wide  atmospheric  changes 
whose  causes  are  not  fully  understood,  give  rise  to  waves  of 
alternating  high  and  low  barometric  pressure,  largely  con- 
verting rectilinear  or  slightly  curved  wind-motion  into  whirls 
or  "  cyclones  "  !  ranging  from  a  thousand  to  over  two  thou- 
sand miles  in  diameter.  These  in  the  case  of  low-pressure 
waves  or  centers,  tozvard  which  the  air  flows  from  the  outside, 
revolve  in  the  direction  contrary  to  the  movement  of  the  hands 

1  This  designation  is  popularly  and  incorrectly  applied  to  the  comparatively 
limited,  but  very  violent  and  destructive  rotary  storms  or  whirlwinds  which 
originate  locally  on  the  heated  plains  of  the  Middle  West  of  the  United  States,  and 
are  almost  always  accompanied  by  violent  electric  phenomena.  These  should 
properly  be  called  tornadoes.  At  sea  such  whirlwinds  give  rise  to  waterspouts,  in 
deserts  to  sand  storms. 


CLIMATE. 


293 


of  a  clock,  and  commonly  produce  rain  in  their  east  portion. 
A  high-pressure  wave  or  center,  from  which  the  air  naturally 
flows  toward  the  outside,  will  usually  bring  about  an  "  anti- 
cyclone "  area  with  fair,  and  in  winter  cold  ("blizzard") 
weather,  the  direction  of  the  whirl  being,  in  this  case,  the  re- 
verse, or  in  the  same  direction  as  the  hands  of  a  clock.  Both 
cyclones  and  anti-cyclones  move  in  North  America  from  west 
to  east,  mostly  entering  from  the  Pacific  Ocean  off  the  north- 
west coast  and  traversing  the  continent  with  a  slight  south- 
east (or  in  the  case  of  cold  weather  almost  south)  trend,  with 
a  velocity  of  twenty  to  thirty  miles  an  hour ;  until  upon  reach- 
ing the  region  of  the  Great  Lakes  they  generally  turn  north- 
eastward and  pass  into  the  Atlantic  Ocean  from  the  New  Eng- 
land and  Canada  coasts. — It  is  upon  these  general  facts, 
roughly  outlined  here,  that  the  weather  forecasts  are  in  the 
main  based ;  taking  into  consideration,  of  course,  the  local  or 
regional  conditions,  topography,  etc.,  which  modify  the  appli- 
cation of  the  general  rules. 

In  the  southern  hemisphere,  the  air-movements  substantially 
correspond  to  those  observed  in  the  northern,  so  far  as  not 
modified  by  mountain  chains;  as  is  especially  the  case  in  South 
America. 

INFLUENCE  OF  TOPOGRAPHY. 

Rains  to  Windward  of  Mountain  Chains. — The  surface  fea- 
tures or  topography  of  the  regions  traversed  by  the  air  cur- 
rents or  winds  may  materially  modify  both  their  direction  and 
their  physical  condition,  especially  as  to  moisture  and  temper- 
ature. Mountain  chains  may  deflect  them,  or,  causing  the  air 
currents  to  rise  on  their  slopes,  and  thus  to  cool  by  expansion, 
the  moisture  these  bring  with  them  from  the  sea  may  be 
partially,  or  sometimes  almost  wholly,  deposited  in  the  form  of 
rain  or  snow;  chieily  °n  the  windward  slopes.  Then,  continu- 
ing across  the  range,  the  air  deprived  of  most  of  its  moisture 
cannot  readily  yield  up  more;  hence  the  scarcity  of  rain — 
"arid  climate" — under  the  lee  of  mountain  chains;  as  in  the 
Great  Basin  between  the  Sierra  Nevada  and  Cascade  ranges 
on  the  one  hand  and  the  Rocky  Mountains  on  the  other,  and 
also  on  the  Great  Plains  under  the  lee  of  the  latter.  The 


294 


SOILS. 


abundant  rainfall  between  the  Mississippi  river  and  the  At- 
lantic coast  is  due  to  the  moist  winds  coming  from  the  warm 
waters  of  the  Gulf  of  Mexico  and  Caribbean  sea,  whose  access 
is  not  interfered  with  by  any  cross-ranges  of  mountains.  But 
the  Great  Plains  lying  between  the  Mississippi  and  the  Rocky 
Mountains  are  not  within  the  sweep  of  the  Gulf  winds,  whose 
trend  is  SW  to  NE;  while  they  are  equally  out  of  reach  of 
moisture  from  the  Pacific,  all  that  having  been  successively  de- 
posited on  the  intervening  mountains;  hence  their  deficient 
rainfall. 

Northward  of  the  temperate  zone  the  rainfall  generally  de- 
creases as  we  approach  the  arctic  regions ;  except  where  the  in- 
fluence of  warm  ocean  currents  to  windward  creates  com- 
paratively local  exceptions,  as  in  the  case  of  Norway  and 
Alaska. 


FIG.  52. — Composite  Curve  showing  distribution  of  Rainfall  in  Europe,  Africa  and  America  pro- 
jected on  100  Meridian  W.  L. 

The  general  Distribution  of  Rainfall  on  the  globe  is  well 
shown  in  the  annexed  diagram,  which  is  copied  by  permission 
of  the  author  from  his  treatise  on  the  "  Evolution  of 
Climates,"  x  and  represents  the  mean  deduced  from  data  given 
in  the  Atlas  of  Meteorology  by  J.  G.  Bartholomew.  It  is  a 
composite  curve  derived  from  the  consolidation  of  four  curves 
showing  the  distribution  of  rainfall,  viz,  on  the  meridians  of 

1  "  The  Evolution  of  Climates";  by  Marsden  Manson,  July,  1903;    also  Amer 
Geologist,  Aug.-Oct.  1897. 


CLIMATE. 


295 


2O°E.L. ;  the  west  coasts  of  Europe  and  Africa;  the  3Oth 
meridian  W.L.,  in  the  Atlantic  Ocean;  and  the  west  coasts  of 
North  and  South  America,  projected  on  the  plane  of  the  looth 
meridian  W.L.  The  latter  curve  corresponds  with  remarkable 
closeness  to  the  mean  curve  here  given.  "  It  is  not  intended 
that  these  curves  should  include  the  rainfall  upon  meridians  on 
which  the  distribution  in  belts  is  interrupted  by  continental 
influences,  and  by  the  irregular  oblique  belts  of  rain  on  the  east 
coasts."  But  it  presents  an  admirable  generalization  upon 
which,  as  a  basis,  the  local  disturbances  may  be  studied. 

It  will  be  noted  that  the  maximum  of  rainfall  in  the  tropi- 
cal rain-belt  lies  several  degrees  to  northward  of  the  equator, 
owing  doubtless  to  the  greater  land  area  in  the  northern  hemi- 
sphere. There  is  thus,  on  the  whole,  a  narrower  belt  of  de- 
ficient rainfall  or  aridity  between  the  tropical  and  northern 
temperate  rain-belts,  than  in  the  southern  hemisphere.  The 
southern  temperate  rain-belt  touches  only  the  extreme  ends  of 
South  America,  Africa  and  New  Zealand;  elsewhere  on  the 
ocean  it  has  not  been  sufficiently  observed  as  yet.  The  zones 
of  rainfall  and  aridity  are,  however,  known  to  be  subject  to 
seasonal  oscillations  of  several  degrees  in  latitude,  owing  to 
the  obliquity  of  the  plane  of  the  ecliptic,  which  shifts  its  posi- 
tion upon  that  of  the  equator. 

Ocean  Currents. — Since  water  as  a  fluid  is  subject  to  the 
same  circulatory  motions  which  cause  winds,  it  is  to  be  ex- 
pected that  ocean  currents  should  exist  corresponding  to  those 
of  the  air,  as  characterized  in  general  above.  Rut  as  water 
warms  so  much  more  slowly  than  air,  its  circulation  would  be 
comparatively  insensible  were  it  not  for  the  effects  produced 
by  the  air  currents  upon  the  surface  of  the  sea,  combined,  as 
in  the  case  of  the  winds,  with  the  effects  of  the  rotation  of  the 
earth.  \Yithout  going  into  the  details  of  the  ocean  currents  in 
the  tropics,  it  may  suffice  to  say  that  owing  partly  to  the 
moving  and  warming  effects  of  winds,  partly  to  the  natural 
circulatory  motion  of  the  water,  two  great  warm  currents  flow 
from  the  tropics  northward,  materially  modifying  what  would 
otherwise  be  the  climates  of  the  coasts  they  touch. 

The  Gulf  Stream. — The  current  most  generally  known  is 
the  Gulf  Stream,  flowing  partly  from  the  Gulf  of  Mexico  and 
the  Caribbean  Sea,  partly  from  outside  of  the  same  along  the 


296  SOILS. 

chain  of  the  Lesser  Antilles,  along  the  southeast  coast  of  the 
United  States  (Florida,  Georgia  and  South  Carolina)  ;  but 
owing  to  its  greater  rotational  velocity  it  is  soon,  like  the 
winds  of  the  same  latitudes,  deflected  from  a  northward  to  a 
NE.  course,  which  carries  it  away  from  the  American  coast, 
to  impart  some  of  its  warmth,  (probably  mainly  through  the 
winds  that  blow  over  it),  to  Great  Britain  and  Ireland,  Scandi- 
navia, and  Western  Europe  generally;  while  the  northern 
American  coast  is  left  to  be  bathed  by  the  icy  polar  current 
flowing  from  the  Arctic  through  Baffin's  Bay,  which  carries 
icebergs  far  to  the  south  in  the  way  of  the  transatlantic  traffic 
between  the  Eastern  States  and  Europe,  and  causes  a  differ- 
ence in  climate  that  is  well  exemplified  in  the  comparison  of 
the  climate  of  New  York  with  that  of  Naples,  both  lying  in  the 
same  latitude;  and  similarly  of  the  bleak  coast  of  Labrador 
with  that  of  Great  Britain. 

The  Japan  Stream. — On  the  eastern  Asiatic  Coast,  a  warm 
current  originating  in  the  Sunda  seas,  flows  off  the  coasts  of 
the  Philippines  and  of  China  and  bathes  the  Japanese  islands ; 
hence  it  is  known  as  the  Japanese  Current,  or  Kuro-siro.  It  is 
partly  this  current  which,  failing  to  pass  into  the  Arctic 
through  the  shallow  waters  of  Behring  strait,  renders  the 
coast  climates  of  the  northwest  coast  of  America  so  much 
milder  and  moister  than  is  that  in  corresponding  latitudes  on 
the  east  coasts  of  both  continents.  Alaska  corresponds  to  Nor- 
way in  its  moist,  foggy  and  relatively  mild  coast  climate;  Brit- 
ish Columbia,  Washington  and  Oregon  participate  in  the  bene- 
fits of  the  tempering  influence  of  the  return  current  of  the 
Kuro-siro.  But  as  this  return  ("Alaska")  current  passes 
southward  into  the  warmer  seas  off  the  California  coast,  its 
influence  is  reversed;  it  becomes  a  cold  current  in  the  warm 
waters  of  the  Pacific,  and  the  warm,  moist  air  of  the  ocean 
being  carried  by  the  westerly  winds  across  this  cold  stream 
which  flows  along  the  shore  of  California,  in  summer  dense 
fogs  are  formed,  which  render  navigation  difficult  and  pro- 
duce a  coast  climate  whose  average  summer  and  winter  tem- 
peratures (c.  g.  at  San  Francisco)  may  differ  by  only  a  few 
degrees,  viz.,  15.5  and  13.0°  C.  (60  and  56°  F.);  so  that  a 
change  of  clothing  from  season  to  season  is  hardly  called  for. 
The  Alaska  Current  leaves  the  immediate  coast  of  California 


CLIMATE. 


297 


off  Pt.  Conception  near  Santa  Barbara,  gradually  losing  it- 
self southwestward,  but  still  tempering  the  tropical  heat  in  the 
Hawaiian  Islands.  Hence  the  coast  climate  is  much  warmer 
and  less  foggy  in  southern  California;  but  throughout  the 
State  in  the  interior  valleys,  screened  from  the  coast  winds  by 
the  Coast  ranges,  the  temperature  in  summer  may  rise  several 
degrees  above  100°  F.  for  days  together;  although,  owing  to 
the  dryness  of  the  air,  the  heat  is  not  oppressive. 

Contrasting  Climates  in  N.  W .  America. — An  even  more 
striking  contrast,  showing  the  effects  of  the  warm  ocean  and 
air  currents,  when  intercepted  by  mountain  chains,  exists  on 
the  Pacific  coast  farther  northward,  as  already  mentioned. 
In  Oregon  and  Washington  first  the  low  Coast  ranges,  and 
then  the  higher  Cascade  mountains,  obstruct  the  eastward 
progress  of  the  westerly  ocean  winds.  The  result  is  a  very 
heavy  rainfall  to  coastward  of  and  within  the  Coast  ranges, 
and  an  almost  equally  heavy  precipitation  on  the  western 
slope  of  the  Cascades.  Standing  on  the  crest  of  the  latter  in 
summer,  one  may  see  to  westward  a  rolling  sea  of  clouds, 
causing  almost  daily  rains ;  while  to  eastward  the  eye  ranges 
over  brown  or  whitish,  dusty  plains  or  rolling  lands,  almost 
destitute  of  tree  growth  and  quivering  with  heat,  under  a 
deep  blue  sky  untroubled  by  clouds  for  months. 

A  somewhat  similar  contrast  is  seen  in  the  Hawaiian  islands, 
which  are  in  the  sweep  of  the  subtropical  northeast  trade 
winds,  and  on  their  windward  (eastern)  slopes  have  abundant 
rains;  while  on  the  leeward  slopes  an  almost  arid  climate  pre- 
vails, calling  for  extended  irrigation. 

Continental,  Coast  and  Insular  Climates. — From  what  has 
been  said  above,  the  striking  differences  of  climate  caused  by 
the  position  of  any  region  with  reference  to  the  sea  or  other 
large  bodies  of  water  on  the  one  hand,  and  to  mountain  chains 
on  the  other,  can  be  readily  understood;  provided  of  course 
that  the  direction  of  the  winds  and  the  trend  of  the  mountain 
chains  be  properly  taken  into  consideration.  Western  coasts 
in  the  temperate  and  subtropical  regions  will  have  a  relatively 
even,  temperate  and  moist  climate  as  compared  with  the  in- 
terior of  continents,  from  which  the  tempering  influence  of 
the  sea  is  cut  off  by  mountain  chains.  Where  no  such  chains 
intervene  the  coast  climate  may  extend  far  inland.  The  lat- 


298  SOILS. 

ter  case  is  that  of  Europe,  where  the  prevailing  westerly  winds, 
warmed  by  the  Gulf  Stream,  temper  the  climate  as  far  east  as 
the  borders  of  Russia,  and  northward  to  Norway;  while  to 
southward  the  warm  waters  of  the  Mediterranean  and  Black 
seas  temper  both  heat  and  cold  in  Spain,  southern  France, 
Italy  and  the  Mediterranean  border  generally.  But  to  east- 
ward, in  Russia  and  Siberia,  the  climate  becomes  "  conti- 
nental "  to  an  extreme  degree,  with  very  cold  winters  and 
very  hot  summers.  The  same  is  true  of  interior  North  Amer- 
ica, wherever  the  continental  divide  cuts  off  the  tempering  in- 
fluence of  the  westerly  winds;  Montana,  the  Dakotas  and  the 
Great  Plains  states  generally  being  examples.  The  climate  of 
the  Mississippi  valley,  as  stated  before,  is  tempered  by  the 
winds  blowing  from  the  Gulf  of  Mexico,  but  with  occasional 
irruptions  of  the  continental  climate  (sometimes  reaching  as 
far  east  as  the  South  Atlantic  coast)  in  the  forms  of  cold 
"  blizzards,"  from  which  the  coast  climates  of  the  Pacific  and 
of  western  Europe  are  practically  free.  The  Atlantic  coast 
of  North  America  (including  the  coast  of  the  Gulf  of  Mexico), 
moreover,  not  unfrequently  suffers  from  the  violent  cyclonic 
storms  that  originate  in  the  Antilles  and  follow  more  or  less 
the  direction  of  the  Gulf  Stream. 

Islands,  differing  from  continents  mainly  in  their  extent, 
and  having  a  relatively  large  proportion  of  coast,  naturally 
have  climates  controlled  essentially  by  the  surrounding  ocean. 
The  insular  or  oceanic  climates  are  therefore,  as  a  rule,  more 
temperate  and  even  than  are  those  of  the  nearest  mainland. 
It  is  often  said  that  the  climate  of  western  Europe  is  "  in- 
sular " ;  and  owing  to  its  position  under  the  lee  of  the  Gulf 
Stream,  this  is  eminently  true  of  Great  Britain. 

Subtropic  Arid  Belts. — Where  the  surface  features  of  the 
land  in  relation  to  the  ocean  and  prevailing  winds  do  not  in- 
terpose special  obstacles,  we  find  to  poleward  of  both  tropics 
a  climatic  belt  of  greater  or  less  width,  in  which  the  annual, 
or  at  least  the  summer  rainfall  is  too  small  to  maintain  annual 
herbaceous  vegetation  throughout  the  season,  even  when  the 
temperature  is  favorable.  These  two  "  arid  "  belts  are  best 
defined  in  Africa,  where  the  northern  one  is  represented  by 
the  Sahara  desert,  lower  Egypt  and  Arabia,  while  the  south- 
ern one  is  exemplified  in  the  Kalahari  desert,  to  northward  of 


CLIMATE.  299 

the  Cape  of  Good  Hope.  The  northern  belt  is  continued  into 
Asia  Minor,  Palestine,  Syria  and  Persia,  and  is  again  manifest 
in  northwestern  India;  but  to  eastward  is  stopped  by  the  in- 
fluence of  the  great  Himalaya  range.  The  plateau  countries 
beyond,  in  Central  Asia,  are  extremely  arid,  largely  by 
reason  of  their  high  elevation. 

In  Australia  the  southern  arid  belt  is  very  strongly  defined. 
In  North  America,  the  arid  belt  is  characteristically  defined  on 
the  Pacific  Coast.  It  embraces  all  but  the  southernmost  point 
of  the  peninsula  of  Lower  California,  with  about  two-thirds 
of  the  State  of  California;  thence  eastward  across  Sonora  and 
Arizona  to  New  Mexico  and  western  Texas.  But  here  the 
influence  of  the  mountain  ranges  and  high  plateaus  obscures 
the  subtropical  belt  as  such,  the  arid  climate  continuing,  east 
of  the  great  Pacific  ranges,  through  Nevada,  Utah,  Wyoming, 
Montana,  Idaho,  and  eastern  Oregon  and  Washington  nearly 
to  the  line  of  British  Columbia  on  the  north,  and  with  gradu- 
ally decreasing  aridity,  into  Colorado,  Kansas,  Nebraska,  and 
the  Dakotas. 

In  South  America  the  rainless  seaward  slopes  of  southern 
Peru  and  northern  Chile  indicate  the  southern  arid  belt ;  but 
here,  the  great  chain  of  the  Andes  intervening,  the  dry  pampas 
of  Argentina,  and  the  Gran  Chaco  of  southwestern  Brazil,  like 
the  Nevada  basin,  though  arid  would  naturally  be  referred  to 
the  moisture-condensing  influence  of  the  Andes  chain,  under 
the  lee  of  which  they  lie.  From  this  cause  the  region  of  de- 
ficient rainfall,  which  on  the  western  coast  ends  to  northward 
of  Santiago  de  Chile,  is  east  of  the  Andes  continued  much 
farther  poleward,  as  in  North  America ;  reaching  into  Pata- 
gonia. 

Utilization  of  the  Arid  Belts. — While,  as  already  explained, 
the  distribution  of  the  rainfall  through  the  year  is  nearly  as 
important  as  its  total  amount,  yet  it  is  evident  that  even  with 
the  minimum  of  twenty  inches  of  total  precipitation  as  the 
measure  for  crop  production,  a  very  large  proportion  of  the 
land  of  the  arid  region  cannot,  even  with  the  most  elaborate 
system  of  water  conservation,  be  supplied  with  sufficient  water 
for  ordinary  crops,  and  must  he  otherwise  utilized,  mainly  for 
pasture  purposes.  This  is  rendered  practicable  to  a  much 
greater  extent  than  might  be  expected,  because  the  rapid  transi- 


300 


SOILS. 


tion  from  the  rainy  to  the  permanent  dry  season  cures  the 
standing  herbage  into  hay,  which  affords  good  grazing  during 
the  rainless  season.  Moreover,  the  use  of  drought-resistant, 
browsing  forage  plants,  both  shrubs  and  trees,  serves  to  sup- 
plement materially  any  deficiency  in  the  supply  of  "  standing 
hay,"  especially  in  case  the  rains  should  toward  the  end  be 
unduly  delayed.  The  same  is  true  of  the  dried  pods  and 
seeds  of  native  herbage,  which  in  some  cases  (bur  clover, 
lupins,  etc.,)  afford  highly  nutritious  additions  to  the  leafy 
forage.1 

1  See  Kept,  of  the  U.  S.  Commissioner  of  Agriculture  for  1878,  pp.  486-488 ; 
Bull.  Nos.  16  and  42,  Wyoming  Expt.  Station  ;  Bull.  No.  150  Calif.  Expt.  Station; 
Bull.  No.  51,  Nevada  Expt.  Station ;  South  Dakota  Station  Bulletins  Nos.  40,  69, 
70,74;  Kansas  Expt.  Station,  Bulletin  No.  102;  New  Mexico  Expt.  Station, 
Bulletin  No.  18 ;  Montana  Expt.  Station,  Bulletin  No.  30 ;  and  others. 


CHAPTER  XVII. 

RELATIONS  OF  SOILS  AND  PLANT  GROWTH  TO  HEAT. 

The  Temperature  of  Soils. — The  rapid  germination  of  seeds, 
as  well  as  the  development  of  plants  to  maturity,  is  essentially 
dependent  upon  the  maintenance  of  the  appropriate  tempera- 
ture. The  temperature  most  favorable  to  germination  or 
growth,  as  well  as  the  degree  of  tolerance  of  high  and  low 
temperatures,  varies  greatly  with  different  plants,  governing 
mainly  what  is  known  as  their  climatic  adaptation.  A  knowl- 
edge of  these  points  with  reference  to  the  several  crops  is 
therefore  of  no  mean  importance  to  the  farmer;  for,  to  a  cer- 
tain extent,  he  can  control  the  temperature  in  the  soil  itself, 
and  he  can  mostly  choose  for  sowing  and  planting,  the  time 
when  the  soil  shall  have  the  proper  temperature  for  rapid 
germination  or  maturity.  As  a  rule,  it  is  not  desirable  to  have 
either  seeds  or  seedling  plants  in  the  ground  for  any  length 
of  time  when  the  temperature  is  too  low  for  active  vegetation; 
for  while  they  rest,  other,  lower  organisms  (fungi  and  bac- 
teria), adapted  to  low  temperatures,  may  continue  in  full 
activity  at  the  expense  of  the  vitality  of  the  crop  plant. 

Water  exerts  controlling  Influence. — Since  the  capacity  of 
water  for  heat  is  approximately  five  times  greater  than  that  of 
the  average  soil,  equal  weights  being  considered,  it  follows 
that  the  temperature  of  soil-water  must  exert  a  controlling 
influence  over  that  of  the  soil.  Taking  the  case  of  a  cubic 
foot  of  loamy  soil,  fully  saturated  with  water,  in  which  one- 
third  of  the  volume  may  be  assumed  to  be  water:  the  weight 
of  the  dry  soil  being  about  eighty  pounds  per  cubic  foot,  cal- 
culation shows  that  the  amount  of  heat  required  to  raise  the 
temperature  of  the  water  contained,  one  degree,  will  be  fully 
twice  as  great  as  for  that  required  for  the  soil  itself.  It  is 
thus  obvious  that  the  control  of  soil-temperature  is  largely 
dependent  upon  the  control  of  the  water-content  of  the  same, 
which  has  been  discussed  in  a.  former  chapter.  Even  in  the 

301 


302 


SOILS. 


condition  of  moisture  known  to  be  most  favorable  to  plants, 
viz.,  one-half  of  the  maximum  water  capacity,  the  influence  of 
the  water-content  upon  the  temperature  will  still  be  as  great 
as  that  of  the  entire  soil  mass.  This  consideration  emphasizes 
the  importance  of  such  control. 

Cold  and  Warm  Rains. — It  is  not  surprising  then  that  the 
occurrence  of  cold  or  warm  rains  or  the  use  of  cold  or  warm 
irrigation  water  at  critical  periods,  may  largely  determine  the 
success  or  failure  of  the  crop.  It  is  well  known  that  the  oc- 
currence of  a  cold  rain  after  vegetation  has  started  actively  in 
early  spring,  may  not  only  destroy  the  season's  fruit  crop  by 
preventing  the  setting,  or  thereafter  causing  the  dropping,  of 
the  fruit,  but  may  even,  if  the  suppression  of  vegetative  action 
be  continued  for  some  length  of  time,  result  in  serious  injury 
to,  or  death  of  trees.  Widely  extended  disastrous  experience 
of  the  kind  was  had  in  California  in  February  and  March, 
1887,  resulting  in  the  death  of  tens  of  thousands  of  fruit  trees 
and  vines  during  that  and  the  following  season.  It  is  obvious 
that  in  such  a  case  as  this  the  rapid  draining-off  of  the  cold 
water  through  underdrains  would  have  materially  mitigated, 
if  not  wholly  prevented,  such  injury. 

Solar  Radiation. — Aside,  however,  from  such  overwhelming 
influences  as  the  above,  the  soil  temperatures  are  measurably 
controlled  by  the  extent  to  which  they  receive  and  absorb  the 
sun's  heat  rays,  whether  directly  or  through  the  mediation  of 
the  air.  The  direct  effect  of  the  sun's  rays  upon  the  surface 
is,  upon  the  whole,  the  most  generally  potent,  although  warm 
winds  may  occasionally  exert  a  very  strong  influence.  The 
varying  influence  of  the  sun's  rays  depends  primarily  upon 
the  change  of  seasons,  which  themselves  result  from  the  vary- 
ing angles  at  which  the  sun's  rays  strike  the  surface;  as  well 
as  upon  the  duration  of  the  day.  The  greater  or  less  cloud- 
iness or  fogginess  of  the  sky,  of  course,  exerts  a  decided  effect 
in  this  connection. 

TJic  Penetration  of  the  Sun's  Heat  into  the  Soil. — In  the 
temperate  regions  of  the  earth  the  daily  variations  of  temper- 
ature cease  to  be  felt  at  depths  ranging  from  two  to  three  feet, 
according  to  the  nature  of  the  soil  material  and  its  more  or  less 
compacted  condition.  The  monthly  variations,  of  course, 


RELATIONS  OF  SOILS  TO  HEAT. 


303 


reach  to  greater  depths ;  while  the  annual  variations  do  not 
disappear  in  the  temperate  zone,  e.  g.,  at  Paris,  Zurich  and 
Brussels,  at  a  less  depth  than  seventy-five  feet.  At  these 
depths  of  constant  temperature  we  find  approximately  the 
same  temperature  as  that  which  we  can  deduce  from  the  ther- 
mometric  observations  as  the  annual  mean.  From  similar 
causes  the  mean  annual  temperature  of  any  place  may  be  ap- 
proximately deduced  from  the  observation  of  the  water  of 
wells  and  springs  derived  from  moderate  depths.  For  below 
the  level  of  constant  annual  temperature  the  latter  begins  to 
ascend  steadily  as  we  progress  downward,  owing  to  the  in- 
terior heat  of  the  earth. 

Change  of  Temperature  with  Depth. — The  following  table 
of  observations  made  at  Brussels  illustrates  the  decrease  of 
annual  range  of  temperature  with  depth : 

At  feet :  Average  temperature.  Annual  range. 

3-25 7-2°  C.  10.5°  C. 

15-6  13-5°  C.  4-5°C. 

30.8   16.4   C.  i-3°C. 

75.0  17.0   C.  0.0°  C. 

It  is  interesting  to  compare  with  this  record  that  of  a  well 
sunk  by  Frmann  at  Yakutzk,  Siberia,  where  the  mean  annual 
temperature  is — 9.7  C.  (  14.6  F. ).  This  temperature  was 
found  a  few  feet  below  the  surface.  At  50  feet  the  tempera- 
ture was — 7.2  C.  (  19°  F. )  ;  at  145  feet — 5°  Cent.  (23°  F.)  at 
350  feet — .9°  C.  (30.8°  F.)  showing  that  the  ground  was  be- 
low the  temperature  of  freezing  water  for  some  distance  far- 
ther down;  so  that  the  search  for  liquid  water  was  abandoned. 

We  thus  see  that  in  the  Arctic  regions,  owing  to  the  pres- 
ence of  water  in  the  form  of  ice.  the  melting  of  which  impedes 
the  access  of  solar  heat,  the  level  of  no  variation  is  found  at 
the  distance  of  a  fe\v  feet  below  the  surface,  despite  the  great 
variations  in  temperature  between  the  short  but  hot  summer 
and  the  extremely  cold  winter.  In  the  tropics,  also,  the  annual 
temperature-variation  disappears  at  a  less  depth  than  2  feet, 
in  consequence  of  the  very  slight  difference  between  the  two 
seasonal  extremes  of  temperature. 

Surface — Conditions  tJiat  influence  Soil-Temperature. 
Among  these  color  has  already  been  mentioned,  and  to  a  cer- 


304 


SOILS. 


tain  extent  discussed.  While  it  is  true  that,  broadly  speaking, 
dark-colored  soils  absorb  more  of  the  sun's  heat  than  light- 
colored  ones,  other  things  being  equal,  it  must  still  be  under- 
stood, that  the  nature  of  the  color-giving  substance  exerts  a 
very  material  influence  upon  the  amount  of  heat  absorbed. 
Thus  charcoal  is  among  all  known  substances  the  one  absorb- 
ing and  radiating  the  sun's  heat  rays  most  powerfully,  and  all 
kinds  alike;  so  much  so,  that  its  absorbent  power  is  taken  as 
100.  But  other  substances  which  to  the  eye  appear  equally 
black,  have  by  no  means  the  same  absorbing  power.  The  heat 
absorption  by  black  humus  is  high,  though  not  quite  equal  to 
that  of  charcoal ;  and  many  gray  soils,  though  appearing  to  the 
eye  of  rather  light  tint,  really  absorb  more  heat  than  others 
which,  to  our  perception,  have  the  darker  tint,  but  are  colored 
by  other  substances.  Gardeners  and  especially  vine  growers  in 
the  colder  portions  of  Europe  often  take  advantage  of  the 
powerful  absorbing  power  of  carbon  by  spreading  charcoal 
or  black  slate  powder  over  the  surface  of  the  soil  where  early 
maturity  is  specially  desired;  and  slate  powder  is  similarly 
used  by  the  peasants  at  Chamouni  to  hasten  the  melting  of 
the  snow. 

Heat  of  High  and  Low  Intensity. — It  must  also  be  kept  in 
view  that  the  surfaces,  and  especially  the  colors  that  favor  ab- 
sorption of  the  intense  rays  of  the  sun,  may  comport  them- 
selves quite  differently  toward  heat  rays  of  low  intensity,  such 
as  those  thrown  back  from  the  soil  at  night  when  it  cools. 
Were  this  otherwise,  a  soil  that  absorbs  much  heat  in  the 
daytime  would  lose  it  with  corresponding  rapidity  at  night. 
But  this  is  true  only  of  charcoal ;  in  the  case  of  most  other 
substances,  there  is  a  material  difference  in  favor  of  the  re- 
tention of  the  heat,  of  low  intensity,  by  slower  radiation  into 
a  "heat-trapping"  atmosphere. 

Reflection  vs.  Dispersion  of  Heat. — Theoretically,  a  smooth 
surface  reflects  more  heat  than  a  rough  one,  and  warms  much 
more  slowly  by  absorption ;  as  is  strikingly  shown  by  the  use 
of  polished  metal  screens  placed  on  walls  to  prevent  their  being 
overheated  by  a  flue  near  by.  In  the  case  of  soils,  also,  the 
condition  of  the  surface  affects  materially  the  absorption  of 
heat,  but  not  in  accordance  with  the  above  rule  so  far  as  the 


RELATIONS  OF  SOILS  TO  HEAT.  305 

result  is  concerned.  For  it  is  found  that,  other  things  being 
equal,  a  loose  or  cloddy  surface  disperses  in  many  directions 
the  heat  it  receives,  and  does  not  permit  it  to  penetrate  by 
conduction  to  so  great  extent  as  would  a  more  compact  soil, 
whose  smooth  surface  would  waste  less  of  the  heat  received 
by  radiation. 

King  has  called  special  attention  to  the  difference  of  temperature 
existing  between  soils  smoothed  and  compacted  by  a  roller,  and  the 
unrolled  soil  having  a  loose  surface.  He  found  that  the  former  at  a 
depth  of  one  and  a  half  inches  was  as  much  as  5.5°C.  (io°F.)  warmer 
than  the  loose  soil,  and  that  even  at  a  depth  of  three  inches  a  difference 
as  high  as  3.5°C.  (6.5°F.)  existed  between  the  two.  He  observed  at 
the  same  time  that  the  temperature  of  the  air  over  the  unrolled  ground 
was  considerably  warmer  than  above  the  rolled,  thus  corroborating  the 
differences  observed  in  the  soil  itself.  But  at  night  the  heat  is  given 
out  more  rapidly  from  the  rolled  than  from  the  unrolled  surface,  the 
latter  acting  as  a  non-conductor  and  keeping  the  soil  warmer  than  that 
of  the  more  compact  rolled  land.  King  gives  as  the  average  difference 
observed  between  rolled  and  unrolled  land  on  eight  Wisconsin  farms, 
i.6°C.  (3°F.)  in  favor  of  the  rolled  land  between  i  and  4  p.m. 

It  will  thus  be  seen  that  the  loose  tilled  layer,  while  im- 
peding the  penetration  of  the  sun's  heat  into  the  deeper  por- 
tions of  the  soil  during  the  day,  on  the  other  hand  serves  to 
retain  it  at  night  better  than  a  more  compact  soil.  This  ob- 
viously places  it  within  the  power  of  the  farmer  to  exert  con- 
siderable control  over  the  soil-temperature  at  critical  times; 
restraining  or  favoring  the  access  of  the  sun's  heat  in  accord- 
ance with  the  requirements  of  the  climate  or  season,  as  the 
case  may  be. 

Influence  of  a  Covering  of  Vegetation,  and  of  Mulches. — A 
cover  of  either  living  or  dead  vegetation  depresses  the  tem- 
perature of  the  soil  as  compared  with  the  bare  land,  as  elabor- 
ately shown  by  Wollny  and  Fbermeyer.  In  the  monthly  aver- 
ages these  differences  rarely  exceed  .8°  C.  (1.5  degrees  F.), 
and  are  mostly  below  .50°  C.  (i°  F.).  but  during  different 
parts  of  the  day  they  may  rise  to  2.2  to  2.5°  C.  (4  to  4.5°  F. ), 
at  4  inches  depth.  In  summer  they  are  greater  than  at  other 
seasons.  Of  course  the  density  of  the  vegetation  or  the  thick- 
ness of  the  mulch  influences  them  materially.  Forests  exert 
20 


3o6  SOILS. 

the  greatest  cooling-  influence  upon  the  soil,  and  next  to  these 
the  dense  herbaceous  crops,  such  as  clover,  and  the  legumes 
generally. 

Influence  of  the  Nature  of  the  Soil-Material. — Aside  from 
the  surface  condition,  the  nature  of  the  material  itself  exerts  a 
certain  influence,  not  only  upon  the  rate  of  introduction  of 
heat,  but  also  upon  the  amount  taken  up.  Thus  quartz  sand 
having  the  highest  density  (greatest  weight  per  cubic  foot) 
and  also  the  highest  capacity  for  heat  among  the  usual  mineral 
soil-ingredients,  will,  mass  for  mass,  experience  a  smaller  rise 
of  temperature  than  would  clay  or  loam  soil,  of  less  density 
or  volume-weight,  and  also  of  lower  heat-capacity.  While 
this  holds  good  theoretically,  differences  corresponding  to 
this  consideration  rarely  occur  in  nature,  for  the  reason  that 
the  much  greater  influence  of  the  mechanical  condition  of  the 
soil  mostly  overbalances  these  effects.  Thus  Wollny  has 
shown  that  while  quartz  is  a  better  heat-conductor  than  clay, 
quartz  cobbles  or  gravel  will  materially  increase  the  tem- 
perature of  the  soil  in  which  they  are  imbedded.  Yet  com- 
pact clay  is  a  better  conductor  of  heat  than  loose  sand ;  hence 
the  latter,  when  exposed  to  the  intense  heat  of  the  summer 
sun  in  the  desert,  becomes  intensely  hot  on  the  surface,  yet  al- 
lows of  the  existence  of  abundant  moisture  at  a  depth  of  ten 
or  twelve  inches;  while  clay  in  the  same  region,  being  usually 
in  a  compacted  condition,  will  show  a  lower  surface-tempera- 
ture and  will  be  warmer  and  drier  at  a  depth  at  which  sand 
will  still  retain  abundant  moisture,  and  be  comparatively  cool 
(See  chap.  13,  p.  257.)  So  much  indeed  depends  upon  the 
state  of  mechanical  division  and  flocculation  in  which  the  sev- 
eral soils  may  happen  to  be,  that  a  hard-and-fast  statement  in 
regard  to  their  relations  to  heat  cannot  and  should  not  be 
given,  as  it  would  only  lead  to  disappointments  and  practical 
mistakes ;  the  more  as  in  all  cases  the  moisture-condition  ex- 
erts an  influence  predominating  by  far  over  that  of  the  dry 
material  itself,  and  this  moisture-condition  is  subject  to  rapid 
changes,  owing  to  intrinsic  differences  in  the  several  classes 
of  soils.  Wollny  states  as  the  result  of  his  experiments,  that 
in  summer  sandy  soils  are  warmest;  then  humous,  lime  and 
loam  soils ;  while  in  winter  humous  soils  are  warmest,  then 
loams ;  and  sand  coldest. 


RELATIONS  OF  SOILS  TO  HEAT.  307 

Influence  of  Evaporation. — In  treating'  of  the  Conserv- 
ation of  Soil  Moisture  (chapter  13),  the  effects,  conditions  and 
control  of  evaporation  from  the  soil  have  already  been  dis- 
cussed from  several  points  of  view ;  so  that  a  summary  review 
of  the  subject  must  suffice  in  this  place. 

It  has  been  stated  above  that  in  the  case  of  an  average  loam 
soil  saturated  with  water,  the  heat  required  to  raise  the  tem- 
perature of  the  water  one  degree  would  be  about  twice  that 
needed  to  so  change  the  dry  soil  material  itself.  But  if  it  is 
required  to  evaporate  the  same  amount  of  water  from  the  soil, 
nearly  ten  (9.667)  times  that  amount  of  heat  will  be  required; 
or  in  the  case  assumed,  twenty  times  as  much  as  would  suffice 
to  raise  the  temperature  of  the  dry  soil  through  an  equal  in- 
terval of  temperature.  While  in  a  few  cases  the  cooling  of 
the  soil  by  evaporation  is  desirable,  in  the  vast  majority  of 
cases  it  is  injurious  to  the  progress  of  vegetation,  and  should 
be  restricted  as  much  as  possible  by  the  means  outlined  in  a 
former  chapter. 

Formation  of  Dew. — There  is,  however,  another  aspect  of 
evaporation  from  the  soil  which  has  been  long  misunder- 
stood, although  the  true  state  of  the  case  was  partially  recog- 
nized long-  ago.  Dew  is  in  common  parlance  said  to  "  fall," 
it  being  supposed  that,  like  rain,  it  is  derived  from  the  atmos- 
phere. While  this  is  partially  true,  inasmuch  as  from  very 
moist,  and  notably  from  foggy  air  dew  is  frequently  deposited 
on  grass  and  foliage  generally,  as  well  as  on  wood  and  other 
strongly  heat-radiating  surfaces;  yet  as  a  matter  of  fact,  in 
by  far  the  majority  of  cases,  as  shown  by  II.  K.  Stockbridge  l 
and  confirmed  by  everyday  observation,  dew  is  formed  from 
the  vapor  rising  from  the  warmer  soil  into  a  colder  atmos- 
phere, and  condensed  on  the  most  strongly  heat-radiating  sur- 
faces near  the  ground,  such  as  grass,  leaves  both  green  and 
dry,  wood,  and  other  objects  first  encountering  the  rising 
vapor.  In  manifest  proof  of  this  it  will  be  noted  that  very 
heavy  dews  may  be  seen  on  the  ground,  when  the  roofs  of 
houses  as  well  as  the  higher  shrubs  and  trees  remain  perfectly 
dry.  In  winter  this  may  be  most  strikingly  seen  in  the 
deposition  of  hoar-frost  in  and  immediately  around  the  cracks 
of  plank  sidewalks,  whose  surface  remains  dry. 

1  "  Rocks  and  Soils,"  pp.  175-189. 


308  SOILS. 

Dew  rarely  adds  Moisture. — Candid  observations  will  con- 
vince any  one,  therefore,  that  in  most  cases  the  supposed  addi- 
tion to  the  moisture  of  the  soil  from  dews  is  an  illusion. 
Whatever  dewdrops  fall  on  the  ground  are  in  general  simply 
the  return  to  the  soil  of  a  part  of  what  came  from  it;  while 
the  dew  that  evaporates  from  the  bedewed  leaves  or  other 
objects  represents  simply  a  delayed  outgo  of  moisture  from 
the  soil,  which  for  a  time  retards  evaporation  direct  from  the 
soil,  and  thus  effects  a  slight  saving  of  moisture. 

But  while  this  is  measurably  true  of  inland  and  especially  of  continental 
areas  like  the  great  plains  of  North  and  South  America,  it  is  also  true 
that  in  deep  moist  valleys,  and  on  the  rainy  and  foggy  coast  regions  of 
continents,  dews  are  found  to  both  fall  and  rise,  not  uncommonly  to 
such  an  extent  as  to  be  equivalent  to  a  not  inconsiderable  aggregate 
precipitation.  Thus  in  the  moist  coast  belt  of  Oregon  and  Washington 
lying  west  of  the  Cascade  range  of  mountains,  the  morning  dews  of 
summer  are  frequently  so  copious  that  the  water  falls  in  showers  from 
the  lower  trees  and  shrubs,  so  as  to  necessitate  the  use  of  water-proof 
clothing  when  traversing  the  woods  in  the  morning,  quite  as  much  as 
though  rain  was  actually  falling.  In  hilly  and  more  especially  in 
mountainous  regions  the  cold  air  descending  from  above  and  flowing 
down  in  the  ravines  will  often  cause  a  heavy  condensation  of  dew  in 
these,  while  the  bordering  ridges,  which  rise  above  the  cold  currents, 
remain  free  from  dew.  These  descending  currents  as  a  rule  not  only 
bring  no  surplus  moisture  with  them,  but  in  their  downward  course 
become  warmer  by  contraction  and  therefore  relatively  drier.  In  these 
cases  also,  therefore,  the  dew  is  purely  moisture  derived  from  the 
ground,  which  in  rising  encounters  the  cold  air  and  is  thus  condensed. 

The  fact  that  dew  is  most  commonly  derived  from  the  soil 
could  have  been  foreseen  from  the  other  fact,  long  ascertained 
and  known,  that  during  the  night  the  soil  is  as  a  rule  warmer 
than  the  air  above  it;  as  has  been  shown  by  the  earlier  ob- 
servers, as  well  as  more  specifically  by  Stockbridge. 

Dew  'within  flic  Soil. — It  is  obvious  that  whenever  dew  is 
formed  above  the  surface  of  the  soil,  the  air  within  the  latter 
must  be  at  or  near  its  point  of  saturation  with  vapor,  as  in 
fact  is  usually  the  case  a  few  inches  below  the  surface.  It 
follows  that  when  a  depression  of  temperature  occurs  within 


RELATIONS  OF  SOILS  TO  HEAT. 


309 


the  soil,  e.  g.,  at  night,  dew  must  be  deposited  within  the  soil 
down  to  the  depth  to  which  the  nightly  variation  reaches,  in- 
creasing at  that  depth  as  the  vapor  from  the  warmer  soil  be- 
low rises,  to  be  in  its  turn  condensed.  There  is  thus  formed 
at  that  level  a  zone  of  greater  moisture,  which  may  sometimes 
be  noted  in  digging  pits,  by  a  deeper  tint,  without  any  cor- 
responding variation  in  the  nature  of  the  soil.  The  daily  re- 
petition of  this  process,  at  varying  depths,  and  its  greater  or 
less  recurrence  at  or  near  the  limit-levels  of  monthly  and  even 
annual  variations,  must  exert  a  not  inconsiderable  influence 
upon  the  vertical  distribution  of  moisture  in  the  soil ;  which 
instead  of  being  usually  found  in  horizontal  bands  or  zones  of 
varying  moisture-contents,  is  usually  remarkably  uniform  for 
considerable  depths,  despite  the  fitfully  recurrent  additions 
from  rains.  It  is  at  least  probable  that  this  process  of  dew- 
formation  within  the  soil  materially  assists  capillarity  in 
effecting  a  measurably  uniform  vertical  distribution  of  mois- 
ture. ( See  also  page  207,  chapter  1 1 ) . 

Plant-development  under  different  Temperature — Condi- 
tions.— In  the  arctic  regions  the  ground,  frozen  in  winter  to 
unknown  depths,  may  thaw  to  only  three  to  five  feet  during 
the  summer,  notwithstanding  the  great  length  and  continuous 
sunshine  of  the  arctic  day.  The  shallow-rooted  arctic  flora 
develops  very  rapidly  under  the  influence  of  the  continuous 
daylight  and  heat,  in  the  course  of  from  five  to  eight  weeks. 
The  seeds  of  these  plants  must,  of  course,  be  capable  of  ger- 
minating at  very  low  temperatures ;  and  as  a  matter  of  fact, 
we  find  that  both  in  the  arctic  regions  and  in  the  higher  mount- 
ains, certain  plants  are  found  growing  and  blooming  on  slopes 
flecked  with  snow;  each  plant  surrounded  by  a  small  circle 
of  bare  ground,  where  the  snow  has  been  melted  under  the 
influence  of  the  dark-tinted  earth  and  leaves.  It  is  clear  that 
here  germination  has  occurred,  the  foliage  has  been  formed, 
and  the  roots  have  been  exercising  their  vegetable  functions, 
in  ground  soaked  with  water  practically  ice-cold. 

Germination  of  Seeds. — \Yhile  wild  plants  of  special  adapta- 
tion may  thrive  in  very  low  (or  high)  temperatures,  it  is  also 
true  that  few  of  our  cultivated  plants  will  germinate,  and  still 
less  grow  thriftily,  at  such  low  temperatures.  The  limit  be- 


310  SOILS. 

low  which  most  cultivated  plants  may  be  considered  as  remain- 
ing practically  inactive  lies  between  4.4  and  7.2°  C.  (40  and 
45°  F.).  Few  tropical  plants  will  germinate  much  below 
23.8°  (75°  F.)  and  in  some  cases  not  below  35°  Cent.  (95° 
F.).  Even  maize  and  pumpkins,  according  to  Haberlandt, 
germinate  most  rapidly  between  35  and  38.3°  C.  (95  and  101° 
F.),  while  for  wheat,  rye,  oats  and  flax  the  best  temperature 
for  germination  lies  between  21.1  to  26.1  (70  to  79°).  Un- 
der the  most  favorable  conditions  of  temperature  and  moisture, 
some  small  seeds  which  readily  absorb  moisture  will  germinate 
in  from  twenty-four  to  forty-eight  hours,  while  at  a  lower 
temperature  they  may  require  from  three  days  to  two  weeks. 
Thus  Haberlandt  found  that  while  oats  would  germinate  in 
two  days  at  a  temperature  of  17.2  to  17.5°  C.  (63°  to  63.5°), 
it  took  a  full  week  for  germination  when  the  temperature  was 
only  5°  C.  (41°  F.).  It  is  obvious  that  seeds  remaining  inert 
in  the  soil  for  such  lengths  of  time  will  be  subject  to  a  variety 
of  vicissitudes  that  may  injure  or  destroy  their  vitality.  There 
are  many  bacteria  and  fungous  parasites  which  at  low  tem- 
peratures are  perfectly  capable  of  attacking  and  destroying  the 
water-soaked  seed.  There  is  thus  for  each  plant,  from  the 
lowest  to  the  highest,  a  certain  temperature  most  favorable  to 
development;  and  both  above  and  below  this,  the  vegetative 
activity  is  seriously  interfered  with  or  wholly  checked.  A 
knowledge  of  these  limits  is  manifestly  of  the  utmost  practical 
importance. 

The  influence  of  too  high  a  temperature  in  preventing  the  germina- 
tion of  cinchona  seed  from  India,  was  curiously  exemplified  when  it 
was  subjected  to  a  supposedly  favorable  steady  temperature  of  23.8°C. 
(75°F.)  under  otherwise  most  favorable  conditions.  Not  a  single  one 
came  up  in  the  course  of  six  weeks,  and  the  box  in  which  it  had  been 
sown  was  put  away  outside  of  the  hothouse  as  a  failure.  Within  two 
weeks  a  full  stand  of  seedlings  was  obtained,  at  temperatures  ranging 
between  12.7  and  i5.5°C.  (55°  and  6o°F.).  The  fact  that  the  cinchona 
is  a  tree  of  the  lower  slopes  of  the  Andes  (three  to  five  thousand  feet) 
although  at  home  strictly  within  the  tropics,  explains  the  apparent 
anomaly. 


PART  THIRD. 

CHEMISTRY  OF  SOILS. 


CHAPTER  XVIII. 

THE  PHYSICO-CHEMICAL   INVESTIGATION    OF   SOILS  IN  RE. 
LATION  TO  CROP  PRODUCTION. 

THE  chemical  constituents  of  soils  have  been  incidentally 
mentioned  and  discussed  above,  both  in  connection  with  the 
processes  of  soil-formation,  and  with  the  minerals  that  mainly 
participate  therein.  The  manner  of  their  occurrence  and  their 
relations  to  plant  life,  so  far  as  known,  must  now  be  consid- 
ered more  in  detail. 

HISTORICAL  REVIEW  OF  SOIL  INVESTIGATION. 

While  the  obvious  importance  of  the  physical  soil-conditions 
has  long  ago  rendered  them  subjects  of  close  study  by  Schiib- 
ler  l  Boussingault  and  others,  the  chemistry  of  soils  was  very 
generally  neglected  for  a  considerable  period,  after  the  hopes 
at  first  entertained  by  Liebig  that  chemical  analysis  would 
furnish  a  direct  indication  and  measure  of  soil  fertility,  had 
been  sorely  disappointed  in  respect  to  the  only  soils  then  in- 
vestigated, viz.,  the  long-cultivated  ones  of  Europe.  The  re- 
sults of  chemical  analysis  sometimes  agreed,  but  as  often 
pointedly  disagreed,  with  cultural  experiences ;  so  that  after 
the  middle  of  the  nineteenth  century,  but  few  thought  it  worth 
while  to  occupy  their  time  in  chemical  soil  analysis. 

Popular  forecasts  of  Soil  1 'allies. — In  newly-settled  coun- 
tries, and  still  more  in  those  yet  to  be  settled,  the  questions  of 
the  immediate  productive  capacity,  and  the  future  durability  of 
the  virgin  land  are  the  burning  ones,  since  they  determine  the 
future  of  thousands  for  weal  or  woe.  This  need  has  long  ago 
led  to  approximate  estimates  made  on  the  part  of  the  settler. 

1  The  early  work  of  Schiihler  on  soil  physics,  published  at  Leipzig  in  1838 
under  the  title  of  "  Grundsiitze  der  Agrikulturchemie  "and  now  almost  inaccessible 
outside  of  old  libraries,  is  remarkable  as  having  anticipated  very  definitely  much 
that  has  since  been  brought  forward  and  elaborated  anew.  He  is  really  the  father 
of  agricultural  physics. 


SOILS. 

by  the  observation  of  the  native  growth,  especially  the  tree 
growth;  and  where  this  consists  of  familiar  species,  normally 
developed,  such  estimates  on  the  part  of  experienced  men, 
based  on  previous  cultural  experience,  are  generally  very  ac- 
curate ;  so  much  so  that  in  many  of  the  newer  states  they  have 
been  adopted  in  determining  not  only  the  market  value,  but 
also  the  tax  rate  upon  such  lands,  their  productiveness,  and 
probable  durability  being  a  matter  of  common  note. 

Thus  in  the  long-leaf  pine  uplands  of  the  Cotton  States,  the  scattered 
settlements  have  fully  demonstrated  that  after  two  or  three  years  crop- 
ping with  corn,  ranging  from  as  much  as  25  bushels  per  acre  the  first 
year  to  ten  and  less  the  third,  fertilization  is  absolutely  necessary  to 
farther  paying  cultivation.  Should  the  short-leaved  pine  mingle  with 
the  long-leaved,  production  may  hold  out  for  from  five  to  seven  years. 
If  oaks  and  hickory  are  superadded,  as  many  as  twelve  years  of  good 
production  without  fertilization  may  be  looked  for  by  the  farmer ;  and 
should  the  long-leaved  pine  disappear  altogether,  the  mingled  growth 
of  oaks  and  short-leaved  pine  will  encourage  him  to  hope  for  from 
twelve  to  fifteen  years  of  fair  production  without  fertilization. 

Corresponding  estimates  based  upon  the  tree  growth  and  in 
part  also  upon  minor  vegetation,  are  current  in  the  richer  lands 
also.  The  "  black-oak  and  hickory  uplands,"  the  "  post-oak 
flats,"  "  hickory  bottoms,"  "  gum  bottoms,"  "  hackberry  ham- 
mocks," "  post-oak  prairie,"  "  red-cedar  prairie,"  and  scores 
of  other  similar  designations,  possess  a  very  definite  meaning 
in  the  minds  of  farmers  and  are  constantly  used  as  a  trust- 
worthy basis  for  bargain  and  sale,  and  for  crop  estimates. 
Moreover,  experienced  men  will  even  after  many  years'  cul- 
tivation be  able  to  distinguish  these  various  kinds  of  lands 
from  one  another. 

Cogency  of  Conclusions  based  upon  Native  Growth. — Since 
the  native  vegetation  normally  represents  the  results  of 
secular  or  even  millennial  adaptation  of  plants  to  climatic  and 
soil-conditions,  this  use  of  the  native  flora  seems  eminently 
rational.  Moreover,  it  is  obvious  that  if  we  were  able  to  in- 
terpret correctly  the  meaning  of  such  vegetation  with  respect 
not  only  to  cultural  conditions  and  crops,  but  also  as  regards 
the  exact  physical  and  chemical  nature  of  the  soil,  so  as  to 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS.        315 

recognize  the  causes  of  the  observed  vegetative  preferences', 
we  should  be  enabled  to  project  that  recognition  into  those 
cases  where  native  vegetation  is  not  present  to  serve  as  a 
guide;  and  we  might  thus  render  the  physical  and  chemical 
examination  of  soils  as  useful  practically,  everywhere,  as  is, 
locally,  the  observation  of  the  native  growths.  To  a  certain 
extent,  such  knowledge  would  be  useful  in  determining  the 
salient  characters  of  cultivated  soils,  also ;  and  would  be  the 
more  useful  and  definite  in  its  practical  indications  the  more 
nearly  the  cultural  history  of  the  land  is  known,  and  the  less 
the  latter  has  been  changed  by  fertilization.  For,  so  soon  as 
the  first  flush  of  production  has  passed,  the  question  of  how 
to  fertilize  most  effectually  and  cheaply  demands  solution. 

It  was  from  this  standpoint,  suggested  by  his  early  experi- 
ence in  the  Middle  West  and  subsequently  most  impressively 
presented  to  him  in  the  prosecution  of  the  geological  and  agri- 
cultural survey  of  Mississippi,  that  the  writer  originally  un- 
dertook, in  icS57,  the  detailed  study  of  the  physical  characters 
and  chemical  composition  of  soils.  It  seemed  to  him  incred- 
ible that  the  well-defined  and  practically  so  important  distinc- 
tions based  on  natural  vegetation,  everywhere  recognized  and 
continually  acted  upon  by  farmers  and  settlers,  should  not  be 
traceable  to  definite  physical  and  chemical  differences  in  the 
respective  lands,  by  competent,  comprehensively-trained  scien- 
tific observers,  whose  field  of  vision  should  be  broad  enough 
to  embrace  concurrently  the  several  points  of  view — geological, 
physical,  chemical  and  botanical — that  must  be  conjointly  con- 
sidered in  forming  one's  judgment  of  land.  Such  trained  ob- 
servers should  not  merely  do  as  well  as  the  "untutored 
farmer,"  but  a  great  deal  better. 

"Ecological"  studies. — Yet  thus  far  we  vainly  seek  in  gen- 
eral agricultural  literature  for  any  systematic  or  consistent 
studies  of  these  relations.  \Ye  do  find  "ecological"  lists  of 
trees  and  other  plants,  or  "  plant  associations,"  growing  in  cer- 
tain regions  or  land  areas,  described  in  some  of  the  general 
terms  which  may  refer  equally  well  to  lands  of  profuse  pro- 
ductiveness, or  to  such  as  will  hardly  pay  for  taxes  when  cul- 
tivated. Or  when  the  productive  value  is  mentioned,  the 
probable  cause  of  such  value  is  barely  alluded  to.  even  con- 
jecturally,  unless  it  be  in  describing  the  "  plant  formations  " 


SOILS. 

as  xerophytic,  mesophytic  or  hydrophytic,  upon  the  arbitrary 
assumption  that  moisture  is  the  only  governing  factor ;  wholly 
ignoring  such  vitally  important  factors  as  the  physical  texture 
of  the  soil,  its  depth,  the  nature  of  the  substrata,  and  the 
(oftentimes  abundantly  obvious)  predominant  chemical  nature 
of  the  land.  And  on  the  other  hand,  we  find  even  public  sur- 
veys proceeding  upon  the  basis  of  physical  data  alone,  practic- 
ally ignoring  the  botanical  and  chemical  point  of  view,  and 
inferentially  denying,  or  at  least  ignoring,  their  relevancy  to 
the  practical  problems  of  the  farm.  1 

Early  Soil  Surveys  of  Kentucky,  Arkansas  and  Mississippi. 
— Among  the  few  who  during  the  middle  of  the  past  century 
maintained  their  belief  in  the  possibility  of  practically  useful 
results  from  direct  soil  investigation,  wrere  Drs.  David  Dale 
Owen  and  Robert  Peter,  who  prosecuted  such  work  exten- 
sively in  connection  with  the  geological  and  agricultural  sur- 
veys of  Kentucky  and  Arkansas ;  and  the  writer,  who  carried 
out  similar  work  in  the  states  of  Mississippi  and  Louisiana, 
with  results  in  many  respects  so  definite  that  he  has  ever  since 
regarded  this  as  a  most  fruitful  study,  and  has  later  continued 
it  in  California  and  the  Pacific  Northwest.  This  was  done  in 
the  face  of  almost  uniform  discouragement  from  agricultural 
chemists  until  within  the  last  two  decades ;  with  occasional 
severe  criticisms  of  this  work  as  a  waste  of  labor  and  of  public 
funds. 

Investigation  of  Cultivated  Soils. — All  this  opposition  was 
largely  due  to  the  prejudices  engendered  by  the  futile  attempts 
to  deduce  practically  useful  results  from  the  chemical  analysis 
of  soils  long  cultivated,  without  first  studying  the  less  complex 
phenomena  of  virgin  soils;  and  these  prejudices  persisted 
longest  in  the  United  States,  even  though  in  Europe  the  re- 
action against  the  hasty  rejection  of  chemical  soil  work  had 
begun  some  time  before;  as  is  evidenced  by  the  methods  em- 
ployed at  the  Rothamsted  Experimental  Farm  in  England,  the 
Agricultural  College  of  France,  the  Russian  agronomic  sur- 
veys, and  at  several  points  in  Germany.  In  none  of  these 
cases,  however,  more  than  the  purely  chemical  or  physico- 
chemical  standpoint  was  assumed ;  although  in  Russia  at  least, 

1   Bull.  22,  Bureau  of  Soils,  U.  S.  Dept.  of  Agriculture. 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS.       317 

virgin  soils  were  easily  obtainable  and  their  native  growth 
verifiable;  and  were  actually  in  part  made  the  subject  of  chemi- 
cal investigation. 

In  the  course  of  their  work,  Owen  and  Peter  always  care- 
fully recorded  the  native  vegetation  of  the  soils  collected;  but 
neither  seems  to  have  formulated  definitely  the  idea  that  such 
vegetation  might  be  made  the  basis  of  direct  correlation  of 
soil-composition  with  cultural  experience.  Owen  repeatedly 
expressed  to  the  writer  his  conviction  that  such  a  correlation 
could  be  definitely  established  by  close  study ;  but  early  death 
prevented  his  personal  elaboration  of  the  results  of  his  work. 
Peter  likewise  stoutly  maintained  to  the  last  his  conviction  that 
soil  analysis  was  the  key  to  the  forecasting  of  cultural  possi- 
bilities; but  not  being  a  botanist  he  did  not  see  his  way  to  put 
such  forecasts  into  definite  form. 

Change  of  Views. 

In  the  United  States  as  well,  the  ancient  prejudices  have 
now  gradually  given  way  before  the  urgent  call  for  more  de- 
finite information  than  could  otherwise  possibly  be  given  to 
farmers  by  the  experiment  stations,  most  of  whose  cultural 
experiments,  made  without  any  definite  knowledge  of  the  na- 
ture of  the  soil  under  trial,  were  found  to  be  of  little  value 
outside  of  their  own  experimental  fields.  Even  the  multipli- 
cation of  culture  stations  in  several  states,  unaccompanied  by 
soil  research,  is  found  to  be  a  delusive  repetition  of  the  same 
inconclusive,  random  experimenting,  since  it  takes  into  con- 
sideration only  the  climatic  differences,  but  leaves  out  of  con- 
sideration the  potent  factors  of  soil  quality  and  soil  variations. 
At  most  these  were  usually  mentioned  by  them  in  such  inde- 
finite terms  as  "  a  clay  loam,"  "  a  coarse  sandy  soil,"  "  gray 
sediment  land,"  and  the  like;  frequently  not  even  with  a  state- 
ment of  the  depth  and  character  of  the  subsoil  and  substrata, 
much  less  of  their  geological  derivation  or  correlations.  Thus 
any  one  not  happening  to  he  personally  acquainted  with  the 
land  in  question  would  be  wholly  without  definite  data  to  cor- 
relate the  results  with  his  own  case.  It  is  quite  obvious  that 
even  if  only  to  make  possible  the  identification  of  new  lands 
with  others  that  have  already  fallen  under  cultural  experience, 


318  SOILS. 

and  can  therefore  afford  useful  indications  to  the  new  settler, 
a  close  physical  and  chemical  characterization  of  lands  should 
be  made  the  special  object  of  study  by  the  experiment  stations 
and  public  surveys,  particularly  in  the  newer  states. 

Advantages  for  Soil  Study  offered  by  Virgin  Lands. — 
Among  the  special  advantages,  then,  offered  by  virgin  soils  for 
the  study  of  the  correlations  of  soils  and  crops,  the  usual  exist- 
ence of  a  native  flora,  representing  the  results  of  secular  adapt- 
ation, is  of  fundamental  importance.  As  it  is  at  this  time  still 
historically  known  of  most  lands  west  of  the  Alleghenies  what 
was  their  original  timber  growth,  it  is  clear  that  their  original 
condition  can  still  be  ascertained  by  comparison  with  uncul- 
tivated lands  of  similar  growth,  usually  not  very  far  away; 
and  as  their  cultural  history  also  is  largely  within  the  memory 
of  the  living  generation,  the  behavior  of  such  lands  under  cul- 
tivation is  known  or  verifiable.  Foremost  among  the  data 
thus  ascertainable  is  the  duration  of  satisfactory  crop  produc- 
tion, and  its  average  amount.  To  ascertain  these  surviving 
data  by  inquiry  among  the  farming  population  should  be 
among  the  foremost  duties  of  those  connected  with  soil  sur- 
veys; and  persons  temperamentally  unable  to  enlist  the  farm- 
er's sympathy  and  interest  in  such  inquiries  must  be  consid- 
ered seriously  handicapped,  no  matter  what  their  scientific 
qualifications  may  be.  In  no  quest  is  it  more  literally  true 
that  there  is  no  one  from  whom  the  earnest  inquirer  may  not 
learn  something  worth  knowing. 

Practical  Utility  of  Chemical  Soil-Analysis;  Permanent 
Value  vs.  Immediate  Productiveness. — In  many  existing  trea- 
tises so  much  emphasis  is  given  to  the  alleged  proofs  of  the  in- 
utility  of  chemical  soil  examination  in  particular,  that  a  special 
controversion  of  these  arguments  seems  necessary,  in  connec- 
tion with  a  detailed  statement  of  what  can,  and  in  part  has 
been,  done  in  that  direction.  Hence  the  often-repeated 
allusion,  in  the  sequel,  to  points  bearing  on  this  question. 
Hence,  also,  the  detailed  discussion  of  many  points  which  in 
most  agricultural  publications  are  given  only  passing  notice. 

/;/  all  these  discussions  the  difference  between  the  ascertain- 
ment of  the  permanent-productive  value  of  soils,  as  against 
that  of  their  immediate  producing  capacity,  must  be  strictly 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


319 


kept  in  view.  The  former  interests  vitally  the  permanent 
settler  or  farmer ;  the  latter  concerns  the  immediate  outlook 
for  crop  production,  the  "  Diingerzustand  "  of  the  Germans. 
The  methods  for  the  ascertainment  of  these  two  factors  are 
wholly  distinct,  even  though  the  results  and  their  causes  are 
in  most  cases  intimately  correlated.  The  failure  to  observe 
this  distinction  accounts  for  a  great  deal  of  the  obloquy  and 
reproach  that  has  in  the  past  so  often  been  heaped  upon  chem- 
ical soil-analysis  and  its  advocates. 

PHYSICAL    AND    CHEMICAL    CONDITIONS    OF     PLANT    GROWTH. 

While  it  is  true  that  plants  cannot  form  their  substance  or 
develop  healthy  growth  in  the  absence  or  scarcity  of  the  chem- 
ical ingredients  mentioned  on  page  xxxi  of  this  volume,  it  is 
also  true  that  they  cannot  use  these  unless  the  physical  condi- 
tions of  normal  vegetation  are  first  fulfilled.  Both  sets  of  con- 
ditions are  intrinsically  equally  important  and  exacting  as  to 
their  fulfilment;  and  the  farmers'  task  is  to  bring  about  this 
concurrence  to  the  utmost  extent  possible.  The  chemical  in- 
gredients of  plant-food  can,  however,  be  artificially  supplied 
in  the  form  of  fertilizers,  should  they  be  deficient  in  the  soil; 
but  as  has  been  shown  in  the  preceding  pages,  it  is  not  always 
possible  to  correct,  within  the  limits  of  farm  economy,  phy- 
sical defects  existing  in  the  land.  Hence,  however  important 
is  the  natural  richness  of  the  soil  in  plant-food,  flic  first  care 
should  always  be  given  to  the  ascertainment  of  the  proper  phy- 
sical conditions  in  the  soil,  subsoil  and  substrata.  Without 
these,  oftentimes,  no  amount  of  cultivation,  fertilization  and 
irrigation  is  effective  in  assuring  profitable  cultural  results. 

Condition  of  the  Plant-food  Ingredients  in  the  Soil. — But 
even  the  abundant  presence  of  the  plant-food  ingredients,  as 
shown  by  analysis,  will  not  avail,  unless  at  least  an  adequate 
portion  of  the  same  exists  in  a  form  or  forms  accessible  to 
plants.  Of  course  this  condition  would  seem  to  be  best  ful- 
filled by  the  ingredients  in  question  being  in  the  water-soluble 
condition.  But  in  the  first  place,  plants  are  quite  sensitive  to 
an  over-supply  of  soluble  mineral  salts,  as  is  evidenced  by  the 
injurious  effects  produced  by  the  latter  in  saline  and  alkali 
lands.  Furthermore,  substances  in  that  form  would  be  very 


320 


SOILS. 


liable  to  be  washed  or  leached  out  of  the  soil  by  heavy  rains 
or  irrigation,  and  would  be  lost  in  the  country  drainage.  It 
is  therefore  clearly  desirable  that  only  a  relatively  small  pro- 
portion of  the  useful  soil-ingredients  should  be  in  the  water- 
soluble  or  physically  absorbed  condition,  but  that  a  larger  sup- 
ply should  be  present  in  forms  not  so  easily  soluble,  yet  ac- 
cessible to  the  solvent  action  which  the  acids  of  the  soil  and  of 
the  roots  of  plants  are  capable  of  exercising.  This  virtually 
available  supply  we  may  designate  as  the  reserve  food-store. 
Finally,  there  is  practically  in  all  soils  a  certain  proportion 
of  the  soil-minerals  in  their  original  form,  as  they  existed  in 
the  rock-materials  from  which  the  soil  was  formed.  These 
minerals  being  usually  in  a  more  or  less  finely  divided  or  pul- 
verulent condition,  they  are  attacked  much  more  rapidly  by 
the  chemically-acting  "  weathering "  agencies,  viz.,  water, 
oxygen,  carbonic  and  humus  acids,  than  when  in  solid  masses ; 
and  thus,  transformation  of  the  inert  rock-powder  into  the 
other  two  classes  of  mineral  soil-ingredients  progresses  in 
naturally  fertile  soils  with  sufficient  rapidity  to  produce,  in  a 
single  season,  sensible  and  practically  important  results,  known 
as  the  effects  of  fallowing. 

The  Reserve. — The  nature  of  these  processes  has  been  dis- 
cussed in  chapters  I  to  4;  and  it  will  be  remembered  that  two 
of  their  most  prominent  results  are  the  formation  of  clay,  and 
of  zeolitic-compounds,  the  latter  being,  as  heretofore  stated 
(pp.  36  ff)  hydrous  silicates  of  earths  and  alkalies,  easily  de- 
composable by  acids,  and  also  capable  of  exchanging  part  or 
the  whole  of  such  basic  ingredients  with  solutions  of  others 
that  may  enter  the  soil.  These  zeolitic  compounds  therefore 
fulfil  two  important  functions  in  the  premises,  viz. :  a  ready 
yielding-up  of  part  of  their  ingredients  to  acid  solvents,  and 
a  tendency  to  fix,  by  exchange,  a  portion  or  the  whole  of  the 
soluble  compounds  that  may  be  set  free  in,  or  brought  upon 
the  land.  The  first-mentioned  property  is  of  direct  avail  in 
that  the  soil-humus  forms,  and  the  roots  of  plants  exude,  acid 
solvents  on  their  surface,  and  can  thus  draw  upon  the  reserve 
store  of  food;  the  second  tells  in  the  direction  of  preventing 
the  waste  of  water-soluble  manurial  ingredients  supplied  to, 
or  formed  in  the  soil.  (See  above,  chapter  3,  page  38). 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


321 


The  reserve  food-store  may  then  be  placed  under  the  fol- 
lowing heads : 

Hydrous  or  "  zcolitic  "  silicates,  from  which  dilute  acids 
can  take  up  the  bases  potash,  soda,  lime  and  magnesia.  These 
silicates  may  be  in  either  the  gelatinous  or  powdery  form ;  in 
the  former  case  they  may  also  occlude  water-soluble  sub- 
stances. 

Carbonates  of  lime  and  magnesia,  which  are  readily  dis- 
solved by  carbonated  water  as  well  as  by  the  vegetable  acids. 

Phosphates  of  lime  and  magnesia,  not  very  readily  soluble 
in  carbonated  water,  but  more  readily  attacked  by  the  acids 
of  the  soil  and  of  plant  roots ;  thus  supplying  phosphoric  acid 
to  plants.  The  more  finely  divided  they  are  the  more  readily 
they  are  dissolved ;  some  soils  containing  only  crystalline 
needles  of  apatite  (see  chap.  5,  p.  63)  only  are  nevertheless 
poor  in  available  phosphoric  acid. 

The  natural  phosphates  of  iron  and  alumina  are  practically 
insoluble  in  all  solvents  at  the  disposal  of  vegetation  and 
though  present  in  considerable  amounts  in  some  soils,  (see 
chapter  19,  page  355),  may  be  considered  as  being  permanently 
inert,  and  therefore  not  to  be  counted  among  the  soil  resources 
for  plant  nutrition.  As  yet  no  artificial  process  by  which 
their  phosphoric  acid  can  be  made  available  within  the  soil, 
has  been  discovered. 

IVatcr-soluble  Ingredients. — As  regards  these  it  has  already 
been  explained  that  they  are  largely  retained  in  the  condition 
of  purely  physical  adsorption,  as  in  the  case  of  charcoal  or 
quartz  sand,  through  which  sea  water  filters  and  is  thereby 
partially  deprived  of  its  salts.  But  these  can  be  gradually 
withdrawn  by  washing  witli  pure  water  alone,  and  still  more 
easily  when  stronger  solvents  are  used.  Since  the  soil-water 
is  always  more  or  less  charged  with  carbonic  acid,  and  the 
roots  themselves  secrete  carbonic  as  well  as  stronger  acids  in 
their  absorption  of  mineral  plant-food,  there  is  no  difficulty 
about  explaining  the  manner  in  which  such  physically  con- 
densed ingredients  are  taken  up.1 

1  Whitney  (Hull.  22,  U.  S.  Bureau  of  Soils)  claims  on  the  basis  of  a  large  number 

of  (three-minute)  extractions  of  soils  made  with  distilled  water,  that  these  solutions 

are  essentially  of  the  same  composition  in  all  soils  ;  that  all  soils  contain  enough 

plant-food  to  produce  crops  indefinitely;  and   that   the  differences    in   production 

21 


322  SOILS. 

Recognition  of  the  Prominent  Chemical  Character  of  Soils. 
In  a  former  chapter  the  soils  formed  from  the  several  minerals 
and  rocks  have  been  discussed  in  a  general  manner.  We  can 
as  a  rule  obtain  some  insight  into  the  nature  of  any  soil  which 
we  can  trace  to  its  parent  rock  or  rocks,  if  we  are  acquainted 
with  the  composition  of  the  latter. 

Similarly,  but  in  a  much  more  direct  manner,  we  can  ob- 
tain a  strong  presumption  as  to  the  nature  of  any  soil  by  de- 
termining the  undecomposed  minerals  present  in  it.  In  all 
ordinary  cases  the  presumption  must  be  that  the  decomposed 
portion  of  the  soil  has  been  derived  from  the  minerals  still 
found  in  it.  Of  course  it  may  happen  in  the  case  of  lands  de- 
rived from  widely  distinct  and  distant  regions  that  no  such 
characteristic  minerals  can  be  found ;  this  is  very  commonly 
true  of  the  soils  forming  the  deltas  of  large  rivers,  in  which 
sometimes  the  only  remaining  recognizable  mineral  is  quartz 
in  its  several  forms,  with  occasional  grains  of  such  hardy 
minerals  as  tourmaline,  garnet,  etc.  Apart  from  such  cases, 
the  hand  lens  or  the  microscope  permits  us  to  recognize  in 
most  soils  the  minerals  that  have  mainly  contributed  to  their 
formation,  thus  also  gaining  a  clew  to  their  prominent  chem- 
ical nature. 

Such  recognition  sometimes  involves,  of  course,  a  somewhat 
intimate  knowledge  of  mineralogy;  yet  a  little  practice  will 
enable  almost  any  one  to  identify  the  more  important  soil- 
forming  minerals,  under  the  lens  or  microscope,  according  to 
the  degree  of  abrasion  or  decomposition  they  may  have  un- 
dergone. The  details  of  such  researches  lie  outside  of  the 
limits  of  this  treatise,  but  some  general  directions  on  the  sub- 
ject are  given  farther  on.1 

Acidity,  Neutrality,  Alkalinity. — A  test  never  to  be  omitted 

are  due  wholly  to  differences  in  the  moisture  supply,  which  he  claims  is,  aside  from 
climate,  the  only  governing  factor  in  plant  growth.  The  tables  of  analytical 
results  given  in  Bull.  22  fail  to  sustain  the  first  contention  ;  the  second  is  pointedly 
contradicted  both  by  practical  experience,  and  by  thousands  of  cumulative  culture 
experiments  made  by  scientific  observers  ;  the  third  fails  with  the  second,  except 
of  course  in  so  far  as  an  adequate  supply  of  moisture  is  known  to  be  an  absolute 
condition  both  of  plant  growth,  and  the  utilization  of  plant-food.  It  is  moreover 
well  known  that  it  is  not  water  alone,  but  water  impregnated  more  or  less  with, 
humic  and  carbonic  acids,  that  is  the  active  solvent  surrounding  the  plant  root. 
1  See  Appendix  B. 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


323 


is  that  of  the  reaction  of  the  soil  on  litmus  or  other  test  paper, 
to  ascertain  its  acid,  neutral  or  alkaline  reaction.  Should  the 
latter  occur  quickly  (by  the  prompt  blueing  of  red  litmus 
paper),  "  black  alkali  "  would  be  indicated;  but  a  blueing  after 
20  to  30  minutes  means  merely  that  a  sufficiency  of  lime  car- 
bonate is  present.  An  acid  reaction  (the  reddening  of  blue 
litmus  paper)  of  course  indicates  a  "  sour  "  soil  (see  chap.  8, 
page  122). 

Clicinical  Analysis  of  Soils. — When  the  observations  men- 
tioned above  give  no  very  decisive  results  or  inferences  as  to 
the  soil's  chemical  character,  the  more  elaborate  processes  of 
qualitative  and  quantitative  chemical  analysis  may  be  called  in. 
It  would  seem  at  first  sight  that  these  ought  to  yield  very  de- 
finite results  to  guide  the  cultivator ;  yet  such  is  by  no  means 
always  the  case.  Both  the  previous  history  of  the  land,  and 
the  method  of  anaylsis,  influence  materially  the  practical  utility 
of  the  results  of  chemical  soil  analysis. 

The  cause  of  this  uncertainty  becomes  obvious  when  we 
consider  the  three  groups  of  ingredients  outlined  above,  viz., 
the  insoluble  or  unavailable,  wholly  undccomposed  rock  mine- 
rals;  the  "  reserve,"  consisting  of  compounds  not  soluble  in 
water  but  soluble  in  or  decomposable  by  weak  acids;  and  the 
water-soluble  portion,  either  actually  dissolved  in  the  water 
held  by  the  soil,  or  held  by  the  soil  itself  in  (physical)  absorp- 
tion. While  the  latter  portion  is  directly  and  immediately 
available  to  plants,  the  amounts  thus  held  are  usually  quite 
small,  and  (outside  of  alkali  lands)  would  rarely  suffice  for 
the  needs  of  a  crop  during  a  growing  season.1  This  demand 
must  be  materially  supplemented  by  what  can  be  made  avail- 
able from  the  soil  minerals  and  the  "  reserve  "  by  weathering, 
conjoined  with  the  direct  action  of  the  acids  secreted  from  the 
plant's  root-hairs  upon  the  soil  particles  to  which  they  are 
attached.  It  is  obvious  that  the  greater  or  less  abundance  of 
the  plant-food  in  the  soil-material  upon  which  these  processes 

1  The  investigations  of  King  (On  the  Influence  of  Soil  Management  upon  the 
^Vater  Soluble  Salts  in  Soils  and  the  Yield  of  Crops,  Madison,  1903)  show  that  from 
some  soils  at  least,  a  sufficiency  of  plant-food  ingredients  for  a  season's  crop  may 
be  dissolved  by  distilled  water  alone,  if  the  soil  be  repeatedly  leached  and  dried 
at  iio\  Whether  such  a  supply  can  be  expected  under  field  conditions,  remains 
to  be  tested. 


324 


SOILS. 


may  be  brought  to  bear,  must  essentially  influence  the  ade- 
quacy of  the  plant-food  thus  supplied.  Moreover,  the  greater 
or  less  extent  to  which  these  sources  may  have  been  drawn 
upon  previously  in  the  course  of  cultivation,  will  similarly  in- 
fluence that  adequacy,  on  account  of  the  diminution  of  the 
readily  available  supply. 

Water-soluble  and  Acid-soluble  Portions  most  Important. — 
It  thus  seems  that  while  the  undecomposed  rock  minerals  are 
indicative  of  the  nature  of  the  soil,  but  not  directly  concerned 
in  plant  nutrition,  the  most  direct  interest  attaches  to  the  ivater- 
soluble  portion,  and  the  acid-soluble  reserve.  Both  of  these 
can,  of  course,  be  withdrawn  from  the  soil  by  treatment  with 
acids  of  greater  or  less  strength;  and  it  would  seem  that  if 
we  knew  just  what  is  the  kind  and  strength  of  the  acid  solvent 
employed  by  each  plant,  we  could  so  imitate  their  action  as 
to  determine  definitely  whether  or  not  the  soil  contains  an 
adequate  or  deficient  supply  of  actually  available  food  for  the 
coming  crop. 

We  Cannot  Imitate  Plant-root  Action. — In  this,  however, 
we  encounter  serious  difficulties.  The  acids  secreted  by  the 
plant  roots  are  not  the  only  solvents  active  in  the  dissolution  of 
plant-food ;  as  yet  we  know  the  nature  of  only  a  few ;  and  even 
these,  instead  of  acting  for  a  long  time  (season)  on  a  relatively 
small  number  of  soil  particles  touched  by  the  root-hairs,  can 
in  our  laboratories  only  be  allowed  to  act  for  a  short  time  on 
the  entire  soil-mass.  Clearly,  the  results  thus  obtained  can- 
not be  a  direct  measure  of  the  amount  of  plant-food  which  a 
plant  may  take  up  in  a  given  time;  we  can  only  gain  com- 
parative figures.  These,  however,  can  be  utilized  by  com- 
parison with  actual  cultural  experience  obtained  in  similar 
cases. 

Cultural  experience  must,  of  course,  be  the  final  test  in  all 
these  questions;  and  it  is  generally  more  fruitful  to  investi- 
gate the  causes  underlying  such  actual  practical  experience, 
than  to  attempt  to  supply,  artificially,  the  supposed  conditions 
of  plant  growth.  The  latter  are  so  complex  and  so  difficult 
of  control,  that  the  results  obtained  by  synthetic,  small-scale 
experiments  are  constantly  liable  to  the  suspicion  that  they 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


325 


are  partly  or  wholly  due  to  other  causes  than  those  purposely 
supplied  by  the  experimenter. 

Analysis  of  Cultivated  Soils, — It  is  also  clear  that  in  view  erf  the  in- 
evitable complexity  of  the  conditions  governing  vegetable  growth,  we 
should  whenever  feasible  proceed  from  the  more  simple  to  the  more 
complex.  The  failure  to  conform  to  this  rule  in  soil  investigation  has 
been  the  cause  of  an  enormous  waste  of  energy  and  work  bestowed,  at 
the  very  outset,  upon  the  most  complex  problem  of  all,  viz.,  the  investi- 
gation of  soils  long  cultivated  and  manured ;  lands  which,  having  been 
subject  perhaps  for  centuries  to  a  great  and  wholly  indefinite  variety  of 
crops  and  cultural  practices,  had  thereby  become  so  beset  with  artificial 
conditions  that  without  a  previous  knowledge  of  what  constitutes  the 
normal  regime  in  natural  soils,  the  correlation  of  their  chemical  consti- 
tion,  as  ascertainable  by  our  present  methods,  with  their  production 
under  culture,  became  as  complex  a  problem  as  that  of  motions  of  three 
mutually  gravitating  points  in  space.  Neither  can  be  solved  by  the 
ordinary  processes  of  analysis,  chemical  or  mathematical.  Nevertheless, 
though  it  was  at  one  time  contended  that  the  minute  proportion  of 
plant-food  ingredients  withdrawn  from  soils  by  cultivation  could  not  be 
detected  by  quantitative  analysis,  numerous  examples  have  shown  that 
with  our  present  more  delicate  methods  this  can  in  most  cases  be  done, 
though  not  always  after  a  single  year's  crop. 

Mftliods  of  Soil  Analysis. — The  more  or  less  incisive  solvent  agents 
used  in  extracting  a  soil  for  analysis  will  of  course  produce  results 
widely  at  variance  with  each  other.  When  fusion  with  carbonate  of 
soda,  or  treatment  with  fluohydric  acid  is  resorted  to,  we  obtain  for 
each  soil-ingredient  the  sum  of  all  the  amounts  contained  in  each  of 
the  three  categories — the  unchanged  minerals,  the  zeolitic  "  reserve," 
and  the  water-soluble  portion.  It  was  early  recognized  that  the  results 
of  such  analyses  bear  no  intelligible  relation  to  the  productive  capacity 
of  soils;  for  pulverized  rocks  of  many  kinds,  or  volcanic  ashes  freshly 
ejected  and  notoriously  incapable  of  supporting  plant  growth,  might  be 
made  to  give  exactly  the  same  composition.  The  amounts  of  plant- 
food  ingredients  thus  shown  might  be  several  hundreds  or  thousands  of 
times  greater  than  what  one  crop  would  take  from  the  soil,  and  yet  not 
an  ear  of  grain  could  be  produced  on  the  material.  The  only  case  in 
which  any  useful  information  could  be  thus  obtained  would  be  that  of 
the  absence,  or  great  scarcity,  of  one  or  more  of  the  plant-food  in- 
gredients. 


326  SOILS. 

The  next  step  was  to  use  in  soil  analysis  acids  of  such  strength  as  to 
dissolve  all  the  zeolitic  (and  water-soluble)  portion,  leaving  the  un- 
weathered  soil  minerals  behind ;  it  being  assumed  that  the  prolonged 
action  of  the  roots  and  soil-solvents  would  in  the  end  act  similarly  to 
the  acids  employed,  such  as  chlorhydric  or  nitric  acids. 

But  here  also  the  results  of  analysis  very  commonly  failed  to  cor- 
respond to  cultural  experience  in  the  case  of  cultivated  soils ;  which 
frequently  failed  utterly  to  produce  satisfactory  crops  even  when  the 
acid-analysis  had  shown  an  abundance  of  plant-food  ingredients.  Upon 
this  evidence,  this  method  of  soil  investigation  was  also  condemned  as 
being  of  little  or  no  practical  utility ;  and  this  has  ever  since  been  a 
widely  prevalent  view. 

The  preferable  investigation  of  cultivated  soils  was  due  to 
the  fact  that  they  are  practically  the  only  ones  available  in  the 
countries  where  the  study  of  agricultural  science  was  then 
being  prosecuted;  and  the  paucity  of  useful  results  there 
achieved  discouraged  the  undertaking  of  similar  researches 
where,  as  in  the  United  States,  the  materials  for  the  investiga- 
tion of  the  simpler  cases — those  of  unchanged,  natural  or 
virgin  soils — were  readily  accessible.  It  was  not  apparent  on 
the  surface  that  the  indefinitely  varied  conditions  introduced 
by  long  culture  would  inevitably  cause  this  lack  of  definite 
correlation  between  the  immediate  productive  capacity  of  a 
soil  and  the  composition  of  its  acid-soluble  portion,  and  that 
yet  the  same  might  not  be  true  of  natural,  uncultivated  soils, 
which  have  all  been  subjected,  alike,  only  to  the  natural  pro- 
cesses of  weathering,  and  to  the  annual  return  of  nearly  the 
whole  of  the  ingredients  withdrawn  by  plant  growth. 

Following  the  failure  of  the  treatment  with  strong  acids  to 
yield  with  cultivated  soils  results  definitely  correlated  with 
cultural  experience,  numerous  attempts  were  made  to  gain 
better  indications  by  the  employment  of  weaker  acid  solvents. 
The  pure  arbitrariness  of  such  diluted  solvents  was  equaled 
by  the  total  indefiniteness  and  irrelevance  of  the  results  with 
different  soils.  Only  two  rational  alternatives  seem  to  re- 
main, viz.,  either  to  push  the  extraction  to  the  full  extent  be- 
yond which  action  becomes  so  slow  as  to  clearly  exclude  any 
farther  effective  action  of  plant  acids ;  or  else  to  use  the  latter 
themselves  at  such  strengths  as  by  actual  experiment  is  found 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS.       32; 

to  exist  in  their  root  sap.  The  first  alternative  aims  to  ascer- 
tain the  permanent  productive  values  of  soils ;  the  latter  to  test 
their  immediate  productive  capacity.  Both  alternatives  are 
purely  empirical,  and  derive  their  only  claim  to  practical  value 
from  their  accordance  with  practical  experience  (see  chap- 
ter 19). 

THE  SOLVENT  ACTION  OF  WATER  UPON  SOILS. 

The  almost  universal  solvent  power  of  pure  water  has 
already  been  alluded  to  in  chapter  2  (see  p.  18),  and  illustrated 
by  the  analyses  of  drain  and  river  waters.  While  these  con- 
vey a  general  idea  of  the  chief  substances  dissolved  and  car- 
ried off,  the  direct  investigation  of  the  solutions  actually  ob- 
tainable from  the  soil  by  longer  treatment  and  with  no  more 
•\vater  than  is  compatible  with  the  welfare  of  ordinary  crops, 
necessarily  gives  somewhat  different  results.  For  when 
drains  flow  during  or  after  heavy  rains  the  water  has  not  time 
to  become  saturated.  The  following  data  afford  a  clearer  in- 
sight into  the  actual  and  possible  solvent  effects  of  water  in 
the  soil,  and  its  possible  adequacy  to  plant  nutrition  unaided 
by  acid  solvents. 

Extraction  of  Soils  with  Pure  llrater. — Eichhorn  and  Wun- 
der  treated  soils  from  Bonn,  and  from  Chemnitz  (Saxony)  re- 
spectively for  ten  days  and  four  weeks  with  about  one-third  of 
their  weight  of  water;  the  solutions  thus  obtained  contain  in 
1,000,000  parts : 


Bonn. 

Chemnitz. 

Silica  

480 

2  C  7 

Potash    (KuO)      

I  I  C  A 

Soda  (N'a-jO)               ...            

I  I  O 

7O  A. 

Lime    (CaO)                                   

i-X  o 

<S  ;  6 

Magnesia   (MijO)    

•;S  .} 

"  4 

I'eroxid  of  I  ron  (  FcaOi)  

117 

Alumina  (  \1"(  )i)           

> 

> 

Phosphoric  aciil  (  P?(  )•>)      

11  O 

Trace 

Sulfuric  acid  (SO-,)  

lOO  2 

Chi  odd  of  Sodium  (NaCl  )  

^S6 

4*7.6 

328 


SOILS. 


These  figures  differ  widely  in  most  respects  from  those 
given  for  drain  and  river  waters.  Potash  especially  is  far  more 
abundantly  present  in  the  Bonn  soil  solution  than  in  the  drain 
water,  and  so  is  phosphoric  acid ;  while  lime  is  not  widely  dif- 
ferent. Eichhorn  therefore  calculates  that  with  a  reasonably 
adequate  supply  of  water,  these  ingredients  would  fully  suffice 
for  a  full  crop  of  wheat.  The  Chemnitz  soil,  on  the  other 
hand,  does  not  yield  enough  plant-food  for  more  than  a  very 
small  crop  upon  the  same  assumptions. 

Continuous  Solubility  of  Soil-ingredients. — It  seems  to  be 
impossible  to  exhaust  a  soil's  solubility  by  repeated  or  con- 
tinuous leaching  with  water.  This  was  demonstrated  in  1863 
and  1864  by  Ulbricht 1  and  by  Schultze;2  their  general  con- 
clusions have  quite  lately  been  corroborated  by  King,3  as  the 
result  of  extended  and  very  careful  investigations. 

Schultze  experimented  on  a  rich  soil  from  Mecklenburg,  by 
continuous  leaching  with  distilled  water  for  six  days,  one  liter 
passing  every  twenty-four  hours,  with  the  following  results. 

RICH  SOIL  FROM  MECKLENBURG   (Schultze.) 
1,000,000  PARTS  OF  EXTRACTS  CONTAINED  : 


Total  matter 
dissolved. 

Organic  and 
volatile. 

Inorganic. 

Phosphoric 
acid. 

e-jc.o 

740.0 

IQC 

5.6 

Second  do  

I2O.O 

C7.O 

63 

8.2 

Third     do  

261  o 

IOI.O 

i65 

8.8 

Fourth  do      

2O  7  O 

870 

1  20 

7  ? 

Fifth      do  

eT 
2OO.O 

82.0 

178 

6-9 

Sixth      do  

2OO.O 

77.O 

12"? 

4.4 

Total  

I.C7QO 

74O  O 

8  TO. 

41.4 

It  thus  appears  that  while  the  first  extraction  removed  the 
main  portion  of  the  organic  matter,  the  inorganic  matters  dis- 
solved were  not  greatly  diminished  in  subsequent  leachings; 
and  that  phosphoric  acid  continued  to  come  off  to  the  last. 
The  rich  soil  used  in  this  case  gave  results  corresponding  in 


1  Vers.  Stat.  V.  p.  207.  2  Ibid.  VI.  p.  411. 

8  Proc.  Ass'n  Prom.  Agr.  Sci.  1904. 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


329 


general  to  these  from  the  Bonn  soil,  in  the  previous  table. 
From  a  poorer  soil  similarly  treated  by  Ulbricht,  described  by 
him  as  a  ferruginous  sand  from  Dahme,  the  leaching  of  which 
was  continued  for  thirty  days  in  periods  of  three  days  each, 
with  a  total  of  forty  times  its  weight  of  water,  the  results 
were  as  follows : 


SOIL  OF   LOW   PRODUCTION    FROM   DAHME   (Ulbricht). 
THE    SKVERAL    EXTRACTS    CONTAINED    IN    I,OOO,OOO    PARTS: 


First 
Extract. 

Second 
Extract. 

Third 
Extract. 

Fourth 

Extract. 

Fifth 
Extract. 

Sixth 
Extract. 

Potash  

7 

6 

7 

7 

Soda  

41 

1  1 

26 

17 

8 

I.ime  ...   

q6 

70 

c: 

48 

62 

M  agnesia  

14 

10 

q 

7 

8 

Phosphoric  acid  

trace 

*> 

trace 

I 

Totals.. 

i?8 

00 

O7 

So 

7O 

1  1 

It  will  be  seen  that  there  is  a  considerable  difference  both  in 
the  total  amounts  of  matters  dissolved  and  in  the  phosphoric 
acid  taken  out  by  the  water,  as  compared  with  the  rich  soil 
treated  by  Schultze.  The  uniformity  of  the  amounts  of 
potash  removed  at  the  successive  leachings  is  remarkable. 

King's  Results. — The  same  general  features  are  again  strik- 
ingly illustrated  by  King's  results,  as  given  in  the  following 
table.  King's  first  leachings  were  always  made  by  shaking  up 
the  soil  with  ten  times  its  dry  weight  of  water  for  three 
minutes,  then  after  subsidence  filtering  the  solutions  through 
a  Chamberland  (porcelain  biscuit)  filter,  and  then  (without 
evaporation)  determining  the  ingredients  dissolved,  by  very 
delicate,  mostly  colorimetric  methods.  Subsequent  leachings 
were  made  by  packing  the  soil  around  the  filters  and  washing 
with  five  times  the  weight  of  water,  taking  alxitit  fifteen 
minutes  each  time;  but  drying  the  soil  at  uo  degrees  C. 
between  successive  leachings. 


330 


SOILS. 

WATER  EXTRACTION  OF  SOILS  OF   LOW  AND   HIGH   PRODUCTION, 
BY  F.  H.  KING. 

PARTS    PER    MILLION. 


O 

% 

O 

01 

* 

O 

in 

8* 

d 

ez 

~ 

< 

rs 

"3 

r» 

d 

a 

•J? 
'o 

0 

<• 

o 

U 

o" 

JC 

a 

U 

V 

e 

C 

« 

•n 

o. 
o 

0 

3 

0 

•e 

_o 

t/5 

It 

o 

(4 

.ti 

J3 

"3 

rt 

j= 

*^ 

CH 

'"' 

* 

* 

0, 

in 

U 

U 

35 

SOILS  OF   LOW    PRODUCTION. 

Sassafras  sandy  j   i  extraction 

12.62 

74-39 

17.82 

18.03 

74' 

53.84 

13-94 

I 

5.60 

soil.                          i  1  1  extractions 

218.25 

'35-35 

'47  45 

21.76 

64.16 

203.06 

221-33 

2 

170.20 

Norfolk,  North  )   i  extraction 
Carolina  sandy  soil  I  1  1  extractions 

21.17 
166.08 

58.30 
162.98 

22.91 
125.00 

30.64 
27.11 

10.15 
80.34 

42.82 
172.42 

20.42 
148.52 

I 
2 

8.24 

122  20 

Average. 

192.60 

149.20 

136.23 

24.44 

72.25 

126.13 

184.93 

2.- 

146.20 

SOILS   OF   HIGH   PRODUCTION. 

Janesville,  Wis.  J    i  extraction 

25-35 

135.30 

51.72 

55-  '° 

16.96 

"5-43 

29-3I 

2.67 

40.28 

Loam.                      /  1  1  extractions 

3'3-7° 

112030 

500.60 

51.42 

4.8.85 

592.75 

472.95 

O.OO 

414.50 

Hagerst'wn,  Pa.  (    i  extraction 

21.73 

165.25 

76.88 

25.72 

11.51 

187  59 

97.09 

1.67 

21.17 

Clay  loam.               |  1  1  extractions 

3°'-55 

967.80 

463.  15 

96.04 

136.21 

502.82 

620.00 

o.oo 

283.80 

Average. 

307.60 

1044.05 

487.88 

73-73 

277.03 

547-79 

546.48 

o.oo 

349-  '5 

King's  observations  show  strikingly  both  the  continuous 
solubility  of  the  soil,  and  the  differences  between  the  solutions 
derived  from  soils  of  low  and  high  productiveness;  wholly 
negativing  the  contention  of  Whitney  that  the  solutions 
from  different  soils  are  of  practically  the  same  composition.1 
King  also  calls  attention  to  the  fact,  shown  in  other  experi- 
ments made  in  the  extraction  of  soils  without  intermediate 
dryings,  that  the  amounts  extracted  were  very  much  less  in  sub- 
sequent than  in  the  first  extraction ;  doubtless  because  the  evap- 
oration from  the  soil  particles  had  carried  a  large  proportion  of 
soluble  matters  to  the  surface,  whence  it  was  readily  abstracted 
by  the  first  touch  of  the  solvent  water.  At  each  drying  not 
only  are  the  soluble  matters  again  drawn  to  the  surface,  but 
heating  a  soil  even  to  100°  renders  additional  amounts  of  soil 
ingredients  soluble  both  in  water  and  in  acids.  It  can  scarcely 
be  doubted  that  the  intense  heating  which  desert  soils  undergo 
during  the  warm  season  is  similarly  effective;  and  thus  the 
great  productiveness  of  these  soils  under  irrigation,  and  the 
marvelously  rapid  development  of  the  native  vegetation  when 

1  Bulletin  No.  22,  Bureau  of  Soils,  U.  S.  D.  A. 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS.       331 

rains  moisten  the  parched  soil,  is  in  part  at  least  accounted  for 
by  this  immediate  availability  of  a  large  supply  of  plant-food. 
Composition  of  Jancsvillc  loam. — In  connection  with  the 
above  data  given  by  King,  it  is  interesting  to  note  the  compo- 
sition of  the  soil  in  the  above  table  yielding  the  highest  pro- 
portions of  soluble  matter,  when  analyzed  according  to  the 
method  practiced  by  the  writer  (see  chap.  19,  p.  343).  This 
analysis  was  made  under  the  supervision  of  Professor  Jaffa 
in  the  laboratory  of  the  California  Experiment  Station  by 
Assistant  Charles  A.  Triebel. 

Loam  Soil  from  Janesville,  Wisconsin  ;  sample  sent  by  Prof.  F.  H. 
King,  Madison,  Wis. 

This  soil  is  a  light  friable  loam,  resembling  the  northern  Loess  in 
color  and  texture ;  it  is  highly  productive.  It  is  underlaid  at  5  feet  by 
the  drift  gravel  of  that  region,  enclosing  much  calcareous  material, 
which  evidently  has  had  a  large  share  in  the  formation  of  this  soil,  just 
as  is  the  case  in  southern  Michigan. 

The  soil,  when  dried  at  110°  C.,  consisted  of 

CHEMICAL   ANALYSIS   OF   FINE    EARTH. 

Insoluble  matter 69-35 

Soluble  silica 10.89 

Potash  (KOa) 59 

Soda  (NaaO) .04 

Lime  (  CaO) 83 

Magnesia  (  MgO) 51 

Br.  ox.  of  Manganese  '  Mn3O4) .08 

I'eroxid  of  I  ron  ( KejCh 3.60 

Alumina  (AM  >3) 5.26 

Phosphoric  acid  (Pa()31 .06 

Sulfuric  acid   (SOs) .10 

Water  and  organic  matter 8.72 

Total 1 00.03 

It  will  be  noted  that  in  accordance  with  the  interpretation  of  analyses 
of  soils  as  given  in  the  next  chapter,  this  is  a  high-class  soil  in  every 
respect,  except  that  its  content  of  phosphoric  acid  is  only  just  above 
the  lower  limit  of  sufficiency.  But  as  is  also  shown  below,  in  presence 
of  a  large  supply  of  lime  even  lower  percentages  of  phosphoric  acid  are 
adequate  for  long-continued  production  (see  chap.  19,  pp.  354,  365). 
by  rendering  the  substance  more  freely  available  ;  and  that  this  is  true 
in  this  case  is  shown  by  the  result  of  King's  leachings,  in  which  this 
soil  yields  a  maximum  of  419  parts  per  million  as  against  80  and  64 
parts  in  the  poor  soils,  which  at  the  same  time  yield  only  one  fourth  as 
much  of  lime.  Unfortunately  we  have  no  full  analyses  of  these  other 


332  SOILS. 

soils  for  comparison ;  although  they  have  served  as  a  basis  of  comparison 
lor  years  in  the  Washington  Bureau  of  Soils. 

Solubility  of  Soil  Phosphates  in  Water. — The  solubility  of 
the  phosphate  contents  of  soils  has  been  elaborately  investi- 
gated by  Th.  Schloesing  fils.1  He  found  in  the  case  of  a  num- 
ber of  soils  investigated  by  him  that  the  amount  of  phosphoric 
acid  P2O5  in  the  soil-solution  ranged  from  less  than  one  mil- 
lionth (or  one  milligram  per  liter  of  water)  in  a  poor  soil,  to 
over  three  milligrams  in  a  rich  one.  He  also  found  that  for 
one  and  the  same  soil  the  amount  so  found  was  constant,  if 
about  a  week's  time  were  allowed  for  saturation.  He  calcu- 
lates that  while  in  general  the  amount  of  phosphoric  acid  capa- 
ble of  being  supplied  to  the  crop  during  a  growing  season  of 
twenty-eight  to  thirty  weeks  would  suffice  for  but  few  crops, 
the  supply  so  afforded  is  in  no  case  a  negligible  quantity,  fre- 
quently amounting  to  more  than  half  of  the  crop-requirements. 
Experiments  with  various  crops  prove  that  these  dilute  solu- 
tions are  utilized  by  all  of  them,  sometimes  to  the  extent  of 
completely  consuming  the  content  of  the  solution.  The  much 
smaller  content  of  phosphoric  acid  in  drain  waters  is  accounted 
for  by  the  lack  of  time  for  full  saturation  during  the  time  that 
the  flow  lasts.  Whitney,  (Bureau  of  Soils,  Bulletin  22)  has 
extracted  the  soil-solution  by  means  of  the  centrifuge  from 
several  soils ;  the  contents  of  phosphoric  acid  thus  found  are  in 
general  of  the  same  order  as  those  shown  in  the  preceding  table 
by  King,  but  much  in  excess  of  Schloesing's  figures ;  notwith- 
standing the  fact  that  Whitney's  soils  had  been  in  contact  with 
water  for  only  twenty-four  hours.  The  cause  of  this  wide  dis- 
crepancy is  not  clear. 

Practical  Conclusions  from  Water  Extraction. — As  regards 
the  practically  useful  conclusions  to  be  drawn  from  the  ex- 
traction of  soils  with  pure  water,  the  data  given  above,  and 
especially  the  results  obtained  by  King,  seem  to  prove  that 
there  is  a  more  or  less  definite  correlation  between  the  immedi- 
ate productiveness  of  soils  and  the  amount  and  kinds  of  in- 
gredients dissolved ;  especially  in  the  case  of  phosphoric  acid, 
the  adequacy  of  the  supply  of  which  for  immediate  production 

1  Ann.  de  la  Sci.  Agron.,  2de  serie  tome  i,  pp.  416-349;  1899. 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


333 


is  assumed  to  be  thus  demonstrable  by  many  French  chemists. 
Moreover,  a  number  of  King's  results,  tabulated  in  curves, 
exhibit  a  remarkable  general  parallelism  of  the  curves  showing 
totals  of  plant-food  extracted  by  water,  and  actual  crop  pro- 
duction. This  is  the  more  remarkable  since  it  is  known  to  be, 
not  pure  water,  but  such  as  is  more  or  less  impregnated  with 
carbonic  acid  at  least,  that  is  actually  active  in  soil-solution 
and  plant-nutrition.  The  farther  development  of  this  method 
may,  it  would  seem,  lead  to  definite  conclusions  at  least  in  re- 
spect to  the  immediate  productive  capacity  of  cultivated,  and 
perhaps  also  of  virgin  soils.  But  it  is  not  likely  to  give  any 
definite  clew  as  to  the  durability  of  such  lands. 

ASCERTAINMENT    OF    THE    IMMEDIATE    PLANT-FOOD    REQUIRE- 
MENTS OF  CULTIVATED  SOILS  BY   PHYSIOLOGICAL 
TESTS.        PHYSIOLOGICAL    SOIL-ANALYSIS. 

As  has  already  been  stated,  the  quantitative  analysis  of  culti- 
vated soils  by  means  of  strong  acids  affords  a  presumptive  in- 
sight into  their  immediate  productiveness,  and  the  kind  of 
fertilizer  needed  to  improve  it,  only  in  case  of  the  extreme 
deficiency  of  one  or  several  of  the  chiefly  important  plant- 
foods.  The  limits  of  deficiency  of  these  in  virgin  soils  have 
been  discussed  above ;  but  since  in  cultivated  soils  amounts  of 
soluble  plant-food  so  small  as  to  be  beyond  the  limits  of  ordi- 
nary analytical  determinations,  when  distributed  through  an 
acre-foot  of  soil  may,  when  rightly  applied,  nevertheless  pro- 
duce very  decided  effects,  the  indications  thus  obtainable  are 
not  absolute.  Thus  a  dressing  of  150  Ibs.  of  Chile  saltpeter, 
containing  only  about  24  Ibs.  of  nitrogen,  is  capable  of  causing 
the  production  of  a  full  crop  of  wheat  where  otherwise,  even 
under  favorable  physical  conditions,  only  a  fraction  of  a  crop 
•would  have  been  harvested ;  provided,  that  all  the  other  re- 
quisite ingredients  were  present  to  a  sufficient  extent  and  in 
available  form.  Yet  the  amount  of  nitrogen  thus  added  would 
amount,  in  one  acre-font  of  soil  to  only  .ooo8rr,  say  eight  ten- 
thousandths  of  one  percent;  which,  with  the  amounts  of  sub- 
stance usually  employed  in  soil  analysis,  would  be  an  unweigh- 
able  quantity,  and  might  easily  be  overlooked. 

Since  the  amounts  of  potash  and  phosphoric  acid  actually 


334 


SOILS. 


taken  out  of  the  soil  by  one  crop  are  in  general  of  the  same 
order  of  magnitude  as  the  above,  what  is  taken  out  by  one  or 
two  crops  will  usually  fall  within  the  limits  of  analytical  errors, 
especially  of  those  incurred  in  sampling  the  soil.  Yet  that  the 
changes  caused  by  a  number  of  successive  crops  can  be  proved, 
even  by  the  ordinary  methods,  has  been  abundantly  verified. 
For  it  seems  that  the  losses  of  soil  ingredients  in  cultivated 
lands  exceed  considerably  those  calculated  from  the  actual 
drain  represented  by  the  crops. 

Plot  Tests. — There  is,  however,  an  obvious  and  apparently 
simple  method  by  which  every  farmer  might  make  his  own 
fertilizer  tests,  on  a  small  and  inexpensive  scale,  the  results  of 
which  may  afterwards  be  put  in  effect  on  his  entire  land.  It 
is  to  apply  in  proper  proportions  on  plots  (of  say  from  one 
twentieth  to  one  fortieth  of  an  acre),  the  several  plant-food 
ingredients  usually  supplied  in  fertilizers,  singly  as  well  as 
conjointly  writh  each  other,  leaving  check  unfertilized  plots 
around  as  \vell  as  among  them.  By  comparison  with  these, 
the  cultural  results  should  at  once  determine  which  of  the 
fertilizers  can  most  advantageously  be  applied  to  the  land. 
Such  tests  when  carried  out  with  all  the  proper  precautions 
are  often  very  decisive  and  practically  successful.  But  they  so 
frequently  suffer  from  seasonal  influences  (such  as  scanty  or 
excessive  rainfall,  cold  or  heat,  etc.),  inequality  of  soil  condi- 
tions, failure  to  apply  the  fertilizers  at  the  right  time,  or  in  the 
right  way,  the  depredations  of  insects  and  birds,  and  other 
causes,  that  it  generally  takes  several  seasons'  trial  to  obtain 
any  definite  results.  On  level  lands  of  uniform  nature  and 
depth,  they  are  most  likely  to  be  successful ;  while  on  undu- 
lating or  hill  lands  it  is  not  only  very  difficult  to  secure  uni- 
formity of  soil  and  subsoil  on  areas  of  sufficient  size,  but  also 
to  prevent  the  washing  of  fertilized  soil,  or  fertilizer  in  solu- 
tion, from  one  plot  to  the  other  by  the  influence  of  heavy  rains 
or  irrigation;  thus  wholly  vitiating  the  experiments.  In  very 
many  cases,  especially  in  the  arid  region,  the  results  of  such 
trials  have  been  practically  nil,  for  the  reason  that  physical  de- 
fects of  the  soil,  and  not  lack  of  plant-food,  were  the  cause  of 
unsatisfactory  production. 

A  full  examination  of  physical  conditions,  as  outlined  in 
previous  chapters,  should  in  all  cases  precede  the  application  of 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


335 


Scheme  for  Plot-tests  of  Fertilizers. 


336  SOILS. 

fertilizers;  such  examination  will  at  the  same  time  serve  to 
determine  the  greater  or  less  uniformity  of  soil-conditions, 
which  is  of  first  importance  to  the  cogency  of  fertilizer  tests. 
As  a  matter  of  fact,  few  farmers  possess  the  necessary  qualifi- 
cations to  carry  out  such  tests  successfully,  since  their  execu- 
tion requires  a  certain  familiarity  not  only  with  the  principles 
and  methods  of  experimentation,  but  also  the  faculty  and 
practice  of  close  and  reasoning  observation;  which,  unfortu- 
nately, is  not  as  yet  a  part  of  instruction  in  our  schools.  The 
experience  so  often  had  in  co-operative  work  between  experi- 
ment stations  and  farmers  is  cogent  on  this  point. 

Those  desiring  to  do  such  work,  however,  can  make  use  of 
something  like  the  plan  given  above ;  it  being  understood  that 
in  the  case  of  clay  soils,  the  unplanted  paths  left  between  the 
plots  should  be  at  least  two  feet  in  width ;  in  the  case  of  sandy 
soils  the  distance  should  be  not  less  than  three  feet,  and  more 
if  the  plots  are  located  on  a  slope.  The  crop  from  each  plot 
should  if  possible  be  weighed  as  a  whole;  but  if  the  plot  be 
large  and  the  crop  measurably  uniform,  an  aliquot  part,  such 
as  one  fourth,  may  be  weighed  instead.  In  regular  experi- 
mentation the  crops  are  weighed  both  in  the  green  (freshly 
cut)  condition,  and  after  drying.  Since  the  dry  matter  is  the 
real  basis  of  value  in  the  case  of  most  field  crops,  its  weight 
is  the  most  important;  as  the  water-content  of  green  crops 
may  vary  considerably.  But  in  the  case  of  vegetables  as  well 
as  fruit  crops,  not  only  must  the  weight  of  the  fresh  crop  be 
determined,  but  it  should  be  sorted  into  the  "  marketable  "  and 
"  unmarketable  "  sizes  and  qualities.  Failure  to  do  this  may 
vitiate  the  entire  experiment  for  practical  purposes. 

Pot  Culture  Tests. — The  uncertainty  attending  plot  culture 
tests  on  account  of  the  difficulty  of  controlling  seasonal  and 
other  external  conditions,  has  resulted  in  the  extended  adoption 
of  indoor  culture  tests,  usually  conducted  in  zinc  or  "  gal- 
vanized "  cylinders  of  a  size  sufficient  to  contain  from  twelve 
to  twenty  or  more  pounds  of  soil.  These  are  kept  in  a  green- 
house whose  temperature  and  moisture-condition  can  be  regu- 
lated at  will,  and  where  the  soil-moisture  is  wholly  under  con- 
trol. For  investigations  of  the  effects  of  various  kinds  of  plant- 
food  upon  vegetable  development,  this  method  has  served  most 
satisfactorily  and  effectually,  and  striking  photographs  of  re- 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS.       337 

suits  thus  obtained  are  seen  on  all  hands :  for  which  reason,  to 
save  space,  they  have  not  been  introduced  into  this  volume.  It 
seems  at  first  sight  that  the  same  method  should  serve  admi- 
rably to  determine  the  manure-requirements  of  soils  under  con- 
trolled conditions. 

It  must,  however,  be  remembered  that  the  field  conditions  as 
regards  subsoil,  evaporation,  ascent  of  moisture  from  below, 
penetration  and  spread  of  roots,  etc.,  in  other  words,  all  the 
physical  conditions  so  vitally  concerned  in  crop  production, 
except  the  temperature  and  moisture-condition  of  the  soil,  are 
wholly  left  out  of  consideration  in  this  method.  Hence  the 
application  of  the  results  so  obtained  to  actual  field  conditions 
can  only  be  made  with  great  caution,  and  are  often  widely  dis- 
crepant with  actual  experience. 

The  method  has  of  late  been  carried  to  an  extreme  by  the  U.  S. 
Bureau  of  Soils  in  the  proposition  to  supplant  the  large  soil-pots  here- 
tofore used  by  small  paraffined  wire-cloth  baskets,  3X3  inches  in  size, 
in  which  the  soil  to  be  tested  is  sown  with  seeds  which  are  allowed  to 
develop  only  for  three  to  five  weeks  ;  it  being  claimed  that  the  devel- 
opment occurring  during  that  time  is  quite  sufficient  to  indicate  what 
will  be  the  ultimate  outcome  in  crop  production.  But  practical  ex- 
perience has  long  ago  demonstrated  that  these  early  stages  of  growth 
cannot  be  relied  upon  to  show  the  crop  results  to  be  expected.  Yet 
if  this  minute  scale  of  pot-culture  should,  on  further  test,  prove  to  give 
truthful  forecasts  even  in  a  mere  majority  of  cases,  the  facility  with 
which  it  may  be  carried  out  will  entitle  it  to  favorable  consideration. 
A  great  deal  more  proof  is  needed  on  this  point  than  the  confident 
claims  of  the  Bureau  indicate. 

CHEMICAL  TESTS   OF   IMMEDIATE    PRODUCTIVENESS. 

Testing  chemical  soil-character  by  crop  analysis. — Another 
method  for  the  determination  of  immediate  soil  requirements 
has  been  elaborated  by  K.  Godlewski.1  The  principle  upon 
which  this  method  rests  is  that  plants  growing  in  a  soil  defi- 
cient in  available  plant-food  of  any  one  kind  will  in  their  ash 
show  a  corresponding  deficiency,  or  at  least  a  minimum  pro- 
portion of  the  same:  and  that  in  many  cases,  the  nature  of  the 

1  Zeitschr.  Landw.  Vers.  Oesterr.,  1901. 
22 


338  SOILS. 

deficiency  manifests  itself  in  the  form  or  development  of  the 
plant,  so  clearly  as  to  render  chemical  analysis  unnecessary 
(see  below,  chapter  22). 

To  a  certain  extent  the  latter  idea  has  been  and  is  constantly 
being  utilized  in  practice.  It  is  essentially  involved  in  the 
habit  of  judging  of  land  by  its  natural  vegetation ;  and  by  agri- 
cultural chemists  and  intelligent  farmers,  when  they  check  ex- 
cessive growth  of  stems  and  leaf  (indicating  excess  of  nitro- 
gen) by  the  use  of  lime  or  phosphates;  or  prescribe  the  use  of 
nitrogenous  manures  when  a  superabundance  of  small,  un- 
marketable fruit  is  produced.  From  the  coincidence  of  such 
indications  with  the  results  of  the  analyses  of  soils  and  ashes, 
very  definite  and  permanently  valuable  indications  as  to  the 
proper  fertilization  and  other  treatment  of  the  land  may  be 
deduced. 

Godlewski  insists  strongly,  and  with  a  good  deal  of  plausibility,  upon 
the  importance  of  making  such  trials  in  the  open  field  and  not  merely 
in  pots.  While  this  is  true,  it  is  also  true  that  such  field  experiments 
suffer  from  the  same  liability  to  imperfection  as  the  "  plot  fertilizer- 
test  "  plan  just  described ;  viz.,  that  the  season  may  exert  a  much  more 
powerful  influence  than  the  fertilization,  and  the  tests  may  lead  to 
wholly  erroneous  conclusions  unless  the  experiments  are  continued  for 
a  number  of  years,  and  under  skilled  supervision.  But  when  once  the 
normal  ratio  between  the  ash  ingredients  for  a  particular  soil  and 
climatic  region  have  been  ascertained,  the  data  will  be  of  lasting  benefit 
to  agriculture  there,  and  perhaps,  other  things  being  equal,  to  the  world 
at  large. 

H.  Vanderyst  has  discussed  the  entire  subject  of  physio- 
logical soil  analysis  elaborately  in  the  Revue  Generate  Agro- 
nomique  of  Louvain,  1902-3  (Exp't  St.  Record,  April  1904, 
Vol.  8,  page  757)  and  shows  in  detail  the  conditions  under 
which  it  may  be  successful.  Among  these  he  reckons  as  full  a 
knowledge  of  the  chemical  characteristics  of  a  soil  as  can  be 
obtained  by  chemical  analysis. 

Chemical  Tests  of  Immediately  Available  Plant-food. — It  is 
scarcely  doubtful  that  plants  differ  considerably  in  the  energy 
of  their  action  upon  the  "  reserve  "  soil  ingredients;  hence  no 
one  solvent  used  by  the  analyst  could  represent  correctly  the 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


339 


action  of  plant-roots  in  general  upon  the  soil,  even  if  we  could 
give  that  action  the  same  time  (a  growing  season)  and  op- 
portunity afforded  them  in  nature  by  the  root-surface.  We 
are  forced  to  proceed  empirically;  and  among  the  numerous 
solvents  suggested  for  the  purpose  of  soil  extraction,  that  of 
Dyer,  already  mentioned,  viz.,  a  one  per  cent  solution  of  citric 
acid,  making  allowance  for  such  neutralization  as  may  occur 
in  the  soil,  has  seemed  to  the  writer  to  give  results  most  largely 
in  agreement  with  cultural  experience.  Walter  Maxwell  has 
recommended  aspartic  acid  in  lieu  of  citric,  as  approaching 
nearer  to  practical  results,  at  least  with  sugar  cane. 

According  to  the  investigations  of  Dyer,  on  Rothamstead 
soils  of  known  productiveness  or  manurial  condition,  it  ap- 
pears that  when  the  citric-acid  extraction  yields  as  much  as 
.005%  of  potash  and  .010%  of  phosphoric  acid,  the  supply  is 
adequate  for  normal  crop  production,  so  that  the  use  of  the 
above  substances  as  fertilizers  would  be,  if  not  ineffective,  at 
least  not  a  profitable  investment.  These  figures  refer  to  the 
ordinary  field  crops  of  England  and  to  soils  originally  fertile 
and  well  supplied  with  lime.  It  can  readily  be  foreseen  that 
under  other  climatic  and  soil  conditions,  different  figures  may 
have  to  be  established.  So  far  as  the  writer's  experience  goes, 
however,  the  above  figures  are  very  nearly  valid  for  the  arid 
climates  as  well ;  only  the  figures  obtained  for  arid  soils  are 
usually  far  in  excess  of  the  above  minimum  postulates.  Fig- 
ures for  lime  and  nitrogen  are  given  in  chapters  8  and  19. 
But  the  results  obtained  with  the  highly  ferruginous  soils  of 
Hawaii  show  that  under  such  conditions,  figures  far  exceeding 
the  minimum  ones  established  by  Dyer  nevertheless  coexist 
with  need  of  phosphate  fertilization. 


CHAPTER  XIX. 

THE   ANALYSIS   OF   VIRGIN    SOILS   BY    EXTRACTION    WITH 
STRONG  ACIDS. 

As  stated  already,  the  analysis  of  soils  by  extraction  with 
strong  acids  is  intended  to  enlighten  us,  not  in  regard  to  their 
immediate  productiveness  (the  "  Diingerzustand  "  of  German 
agricultural  chemists),  but  as  to  their  permanent  value  or  pro- 
ductive capacity.  As  has  been  seen  in  the  preceding  chapter, 
the  efforts  to  unite  investigators  upon  a  generally  applicable 
and  acceptable  method  for  the  testing  of  immediate  produc- 
tiveness have  not  been  very  successful,  and  the  number  of 
methods  employed  in  different  countries  and  by  different 
chemists  within  the  same  country  are  widely  at  variance,  with 
no  immediate  prospect  of  agreement.  Moreover,  in  most 
cases  the  effort  is  to  combine  both  problems — temporary  and 
permanent  productive  capacity — in  one  method  or  operation; 
which  still  farther  confuses  the  issue. 

Convinced  that  the  only  way  to  unification  lies  in  the  direc- 
tion of  falling  back  upon  a  method  that  is  based  upon  a  natural 
limitation  about  which  there  can  be  no  difference  of  opinion, 
the  writer  has,  in  following  the  lead  of  Owen  and  Robert 
Peter,  endeavored  to  settle  definitely  the  natural  limit  of  the 
action  of  a  suitable  acid  upon  soils,  and  the  time  and  strength 
of  acid  producing  the  maximum,  effect. 

Loughridge's  Investigation. — Systematic  work  on  these 
points  was  undertaken,  at  his  suggestion,  by  Dr.  R.  H.  Lough- 
ridge  in  1871  and  1872.  The  results  of  this  work  were  pub- 
lished in  the  succeeding  year  in  the  Amer.  Journal  of  Science, 
and  in  the  proceedings  of  the  A.  A.  A.  S.  for  1873.  They  seem 
to  be  of  sufficient  general  interest  to  be  reproduced  here. 

The  soil  selected  for  this  purpose  was  a  very  generalized  one, 
representing  large  areas  in  the  states  of  Kentucky,  Tennessee, 
Mississippi  and  Louisiana,  bordering  on  the  east  the  immediate 

340 


THE  ANALYSIS  OF  VIRGIN  SOILS. 


341 


valley  of  the  Mississippi  river,  and  known  locally  as  the 
"  Table  lands ;  "  a  noted  cotton-producing  upland  region.  The 
brown  or  yellow,  moderately  clayey  loam  is  of  great  uni- 
formity throughout  its  region  of  occurrence,  and  is  evidently 
derived  from  such  widely-spread  sources  that  it  represents  no 
special  rock  or  complex  of  rocks.  Its  natural  growth  is  a  mix- 
ture of  oaks  and  hickories,  strong  and  well-developed  trees, 
such  as  any  land-seeker  would  at  once  approve  for  settlement. 
Its  cotton  product  when  fresh  was  a  /po-pound  bale  of  cotton 
lint  per  acre.  It  may  therefore  well  be  considered  a  typical 
generalized  soil  of  the  humid  upland  of  the  Mississippi  valley. 
Its  physical  analysis  is  given  in  chapter  6,  it  being  No.  219 
of  the  table  on  p.  98. 

Strength  of  Acid  used. — Three  different  strengths  of  acid 
were  simultaneously  employed,  viz.,  chlorhydric  of  i.io, 
1.115  and  1.160  density.  With  these  the  soil  was  digested  at 
steam  heat  in  porcelain  beakers  covered  with  watch  glasses  for 
five  days  each,  then  evaporated  and  analyzed  as  usual.  The 
results  were  as  follows : 

ANALYSIS  WITH    ACID    OF    DIFFERENT    STRENGTHS. 


Ingredients. 

Sp.   G.  of  Acid. 

Insoluble    residue  

I.IO 

1.115 

1.160 

71.88 
11.38 

.60 
•13 

•27 
•45 
.06 

5-  '5 
6.84 

.02 
3-'4 

70-53 
12.30 

•63 
.09 

•27 
•45 
.06 
5.1  1 
8.09 

.02 
3-14 

74-15 
9.42 
.48 
•35 
•23 

3 

5.04 

6.22 

.02 
3-'4 

Soluble  silica  

Potash  

Soda  .    .    .    .            

I  ,i  m  e        .  .                  

Magnesia  

Kerric  (  )xid  

A  1  umina  

Sulfuric  arid  

Volatile  matter     

Amount  of  soluble  matter  

100.02 
24.00 

'3-5° 

IOO.69 

27.02 
14.70 

99-29 

22.27 
12.83 

Amount  of  soluble  bases      

It  will  be  noted  that  the  strongest  acid  produced  the  smallest 
amount  of  decomposition  of  the  soil  silicates,  c.  g.  the  silica 
soluble  in  carbonate  of  soda  solution  being  $r/c  less  than  in  the 
case  of  the  acid  of  medium  strength ;  a  result  possibly  due  to 


342 


SOILS. 


some  difficultly-soluble  compound  formed  on  the  surface  of 
the  soil  grains.  The  weakest  acid  had  a  stronger  solvent 
power;  but  the  maximum  effect  was  produced  by  the  acid  of 
1.115  density.  This  being  also  the  most  readily  obtainable,  by 
simple  steam  distillation  of  acid  of  any  other  strength,  the 
writer  adopted  it  as  best  suited  to  the  purposes  of  soil  analysis. 
To  ascertain  the  time  required  for  the  desired  action,  viz., 
the  solution  of  the  plant-food  ingredients  to  the  extent  likely  to 
be  of  any  avail  to  growing  plants,  digestions  of  the  same  soil 
were  made  in  the  same  manner  for  periods  of  I,  3,  4r  5  and  10 
days,  with  the  acid  of  1.115  density.  The  results  were  as  fol- 
lows: 

ANALYSIS  AFTER  DIFFERENT  TIMES    OF    DIGESTION. 


Ingredients. 

No.  of  Days'  Digestion. 

I 

3 

4 

5 

10 

Insoluble  Residue  

76.97 
8.60 

•35 
.06 

.26 
.42 
.04 
4-77 
5-15 

.21 
.02 
3-14 

72.66 
11.18 

•44 
.06 
.29 

•44 
.06 
5.01 
7.38 

.21 
.02 
3-14 

71.86 
11.64 

•57 

•°3 

.28 

•47 
.06 

5-43 
7.07 

.21 
.02 

3-M 

70.53 
12.30 

•63 
.09 

.27 

•45 

.06 

S-11 

7.88 

.21 

.02 
3-M 

7r-79 
10.96 
.62 
.28 
•27 
•44 
.06 
4.85 
7.16 

.21 
.02 
3-'4 

Soluble  Silica  

Potash  

Br  Ox  Manganese  

Sulfuric  acid.  .        ......    .  . 

Votatile  matter  

Total  

99^3 

19.67 
11.05 

100.68 

24.88 
13.68 

100-55 

25-57 
I3-9I 

100.69 

27.02 
14.49 

99.80 

24.87 
13.68 

Amount  of  soluble  matter.. 
Amount  of  soluble  bases... 

While  these  results  pointed  clearly  to  the  five-day  period  as 
being  sufficiently  effective  so  far  as  the  plant-food  ingredients 
are  concerned,  it  was  not  easy  to  understand  why  a  ten-day 
digestion  should  be  less  incisive  than  a  five-day  one.  Instead 
of  repeating  the  ten-day  experiment,  it  was  thought  preferable 
to  re-treat  the  residue  from  the  five-day  digestion  for  five  days 
more.  The  result  was  that  only  more  silica  and  alumina  went 
into  solution — in  other  words,  additional  clay  was  alone  being 
decomposed.  This  being  of  no  interest  in  the  matter  of  plant 
nutrition,  the  five-day  period  was  definitely  adopted  by  the 


THE  ANALYSIS  OF  VIRGIN  SOILS. 


343 


writer  for  his  work;  and  it,  together  with  the  acid  of  1.115 
density,  is  the  basis  of  all  the  results  given  in  this  volume,  ex- 
cept where  otherwise  stated.  There  appeared  to  him  to  be 
no  good  reason  for  the  acceptance  of  the  arbitrary  method  of 
soil-extraction  suggested  by  Kedzie  and  since  adopted  by  the 
Association  of  Official  Agricultural  Chemists;  the  more  as  to 
do  so  would  throw  out  of  comparison  all  the  previous  work 
done  by  Owen,  Peter,  and  himself  and  his  pupils,  which  had 
already  been  definitely  correlated  with  the  natural  conditions 
and  with  cultural  experience.1 

Virgin  Soils  with  High  Plant-food  Percentages  are  Always 
Productive. — In  strong  contrast  to  the  contradictory  evidence 
deduced  from  the  analysis,  by  any  method,  of  cultivated  soils 
when  compared  with  cultural  experience,  it  seems  to  be  gener- 
ally true  that  virgin  soils  showing  high  percentages  of  plant- 
food  as  ascertained  by  extraction  witJi  strong  acids  (such  as 
hydrochloric,  nitric,  etc.),  invariably  prove  highly  productive: 
provided  only  that  extreme  physical  characters  do  not  interfere 
with  normal  plant  growth,  as  is  sometimes  the  case  with  heavy 
clays,  or  very  coarse  sandy  lands. — To  this  rule  no  exception 
has  thus  far  been  found.  The  composition  of  some  represen- 
tative soils  falling  within  this  category  is  given  in  the  annexed 
table,  which  at  the  same  time  conveys  some  idea  of  the  propor- 
tion of  acid-soluble  ingredients  usually  found  in  the  best  class 
of  natural  soils. 

Discussion  of  Table. — It  will  be  noted  in  this  table  that  while 
the  total  of  the  matters  soluble  in  acids  (inclusive  of  silica) 
ranges  from  a  little  below  50  to  over  77  per  cent,  the  total  of 
directly  important  mineral  plant-food  ingredients  (potash, 
lime,  magnesia  and  phosphoric  acid),  constitute  in  moderately 
calcareous  soils  only  from  about  2.5  to  somewhat  over  four 
percent  of  the  whole.  Yet  if  all  these  were  in  available  form, 
the  supply  would  be  abundant  for  many  hundreds  and  even 

1  While  regretting  to  thus  "secede"  from  the  fellowship  of  his  colleagues,  the 
writer  cannot  but  regret  equally  their  voluntary  decision  to  do  over  again,  or 
lightly  reject,  all  that  had  been  done  before  in  correlating  soil-composition  and 
plant-growth.  lie  still  thinks  that  it  is  idle  to  expect  any  unification,  national  or 
international,  of  methods  of  soil  analysis  based  upon  purely  arbitrary  prescriptions, 
unless  previously  shown  to  be  definitely  correlated  with  natural  and  cultural  con- 
ditions ;  as  is  measurably  the  case  with  Dyer's  method. 


344 


SOILS. 


«d              B 

3£"-'8>8r?°£.Soo 

>?    tl   "8 

9 

r 

vC 

•     e 

i 

?? 

";T0><« 

1 

m  0 
•«•  8 

to  0- 

1  r. 
I 

c 

•o 

c3     -S 

o 

8 

M                 t-» 

M 
.X 

«  «9 

0  t« 

•§•& 

ift          Q 

^w                      «         00    0 

^        g 

33 

< 
z 

M 

O 

U  |  c  o 

o- 

iri 

*Jg&S£*SS2? 

-j.        .j. 

'«  3 
>  > 

<•< 

E 
3 

O 

^Fl 

= 

•* 

N           O 

i=ll! 

s? 

«n  O    K  00    O    O^  "100  00    10  -  OC 

^u-i^«  N  o  O^o  r-^*oo  •• 

O    I    OO 

S'jsl 

R.1"" 

*  i 

yw 

\ 

JL 

S    .? 

J5    w*    w 

oo  >o  «      oo  «       »oo            r 

10 

'"   § 

-SVXHk 

|||| 

S> 

O 

2*    * 

^E1"          ?"         ""^              C 

"    i 

UISIANA. 

» 
^Illll 

rt_E  a-jT  g 

0 

•«• 

O 
J 

OT       £       ~~~ 

to  S  "               ""  IT 

00          O 

-       o 

•s-rjf 

g'JJg    7; 

OO 

o 
rx 

tt        0 

0. 

u 

*G 

o       - 
-       o 

1 

3          .     I1 

& 

i. 

3C/3>«.2 

to 

« 

^  o  -    •  -  -    '  ^  o    • 

l-x          O 

1   2 

t 

s      ::::::::::: 
w     

a        ••••••.-... 

o 

i 

"H, 

M 
W 

"o 

z       •    .    .    . 

O          '.'.'.'.'.'.    e>    '•'.     \     '. 
O^..- 

fc. 

V 
JD 

j      :  :  :  :  :  :  %%  :O  j^ 

1 

k. 

9 

S 
1 

1     »%£«  «rt~~~-c«f 

s  l^^i  %i||i 

g^g-Sl&'SlJli 

c  o  o  o-~*-«  u  oj~-.n  3^n 

•g 

O       ^-. 
T3        5 

c      o 
«     H      » 

5        = 

.?              >5 

i 

3 
e 

z 

i 

/ 

'/ 

C 

a 

t.  - 

c 

/ 

'art 
§\ 

•x.lz 

s" 

THE  ANALYSIS  OF  VIRGIN  SOILS. 


345 


thousands  of  crop  years.  For,  one-tenth  of  one  per  cent  in 
the  case  of  the  clayey  soils  of  the  preceding  table  would  amount 
to  about  3500  pounds  per  acre-foot,  and  to  4000  in  the  case  of 
the  sandy  ones.  Hence  the  amount  of  phosphoric  acid  in  c.  g., 
the  Mississippi  delta  soil  from  Houma  would  suffice  for  the 
production  of  about  440  crops  of  wheat  grain  (at  20  bushels 
per  acre)  if  only  one  foot  depth  were  drawn  upon;  but  as  the 
roots  of  grain  easily  penetrate  to  twice  and  half  and  three 
times  that  depth  even  in  the  humid  region,  the  number  might 
be  tripled.  As  a  matter  of  fact,  however,  that  soil  has  pro- 
duced full  crops  for  from  forty  to  fifty  years  only;  yet  this  is 
considered  an  exceptionally  long  duration  of  profitable  pro- 
duction without  fertilization. 

The  first  and  last  soils  in  the  above  list  represent  probably  the  highest 
types  of  productiveness  known.  The  Yazoo  bottom  soil  has  produced 
up  to  one  thousand  pounds  of  cotton  lint  per  acre  when  fresh,  and  is 
still  producing  from  four  to  five  hundred  pounds  after  thirty  years' 
culture.  The  Arroyo  Grande  soil  of  California  with  its  extraordinary 
percentages  of  phosphoric  acid  and  nitrogen,  as  well  as  exceptionally 
high  proportion  of  available  phosphoric  acid  and  potash,  has  made  such 
a  record  of  productiveness,  and  high  quality  of  the  seeds  produced, 
that  it  has  for  a  number  of  years  been  excluded  from  competition  for 
prizes  offered  by  seed-producers  elsewhere,  in  order  to  give  other  sections 
a  chance.  Both  these  soils  are  rather  heavy  clays,  but  readily  tillable 
in  consequence  of  their  abundant  lime-content.  The  remarkably  high 
content  of  acid-soluble  silica,  indicating  the  presence  of  much  easily 
available  /.eolitic  matter,  is  doubtless  connected  with  the  exceptional 
productiveness. 

Experience,  then,  proves  that  lands  showing  such  high 
plant-food  percentages  will  yield  profitable  harvests  for  a  long 
time  without  fertilization,  or  with  only  such  partial  ( returns 
as  are  afforded  by  the  offal  of  crops.  Also  that  when  fertiliza- 
tion comes  to  be  required,  instead  of  supplying  all  the  ingre- 
dients usually  constituting  fertilizers,  only  one  or  two  of  these 
will  as  a  rule  be  actually  needed,  and  even  these  in  smaller 

1  The  Rio  Grande  and  Colorado  bottom  soils  contain  amounts  of  lime  carbonate 
largely  in  excess  of  reqnirements,  2  to  ^  of  that  compound  being  all  that  is 
needed  to  insure  all  the  advantageous  effects  of  lime  in  any  soil  (see  this  chapter, 


346  SOILS. 

amounts  than  in  "poor"  lands;  thus  materially  reducing  the 
expense  of  fertilization.  The  high  production  and  durability 
of  such  lands  therefore  amply  justify  their  higher  pecuniary 
valuation;  for  which  there  would  be  no  rational  permanent 
ground  if  they  required  fertilization  to  the  same  extent  as 
poor  lands.  In  other  words,  if  the  entire  amount  of  soil-in- 
gredients removed  by  crops  had  had  to  be  currently  replaced 
equally  in  all  cases  (as  is  implied  in  the  hypothesis,  advanced 
by  some,  that  the  chemical  composition  of  soils  is  of  no  prac- 
tical consequence),  the  high  prices  which  from  time  imme- 
morial have  been  paid  for  black  prairie  and  rich  alluvial  lands 
as  against  meagre  uplands  and  barrens,  would  have  been  so 
much  money  wasted. 

The  explanation  of  these  advantages  evidently  lies  largely 
in  the  larger  amounts  of  soil  ingredients  annually  rendered 
available  in  rich  soils  by  the  fallowing  effect  of  the  atmospheric 
agencies,  because  of  .the  generous  totals  present.  The  actual 
amounts  of  soil  ingredients  thus  rendered  accessible  to  plants, 
other  things  being  equal,  are  evidently  more  or  less  directly 
proportional  to  the  totals  of  acid-soluble  plant-food  ingredients 
present.  And  if  this  is  true  in  cultivated  lands,  the  inevitable 
conclusion  is  that  the  same  must  be  true  of  virgin  lands;  whose 
productive  capacity  and  duration  can  therefore  be  forecast  by 
such  analyses.  It  will  be  observed  that  the  above  data,  which 
could  be  indefinitely  increased  by  corroborative  analyses,  seem 
to  establish  the  fact  that  about  one  per  cent  of  acid-soluble 
potash,  one  of  lime,  the  same,  or  less,  of  magnesia,  and  .15% 
of  phosphoric  acid,  are  thus  shown  to  be  "  high  "  percentages 
of  these  ingredients  in  virgin  soils. 

It  is  not  easy  to  see  how  the  above  conclusions  can  be  suc- 
cessfully controverted ;  they  are,  moreover,  thoroughly  in  ac- 
cordance with  cultural  experience.  Difficulties  of  interpreta- 
tion arise  mainly  in  the  case  of  medium  soils,  which  show 
neither  very  high  nor  very  low  percentages  of  plant-food ;  and 
which  raise  the  question  of  what  amount  or  percentage  con- 
stitutes "  adequacy  "  of  each  of  the  several  substances. 

Low  Percentages. — On  the  other  hand,  whenever  in  virgin 
soils  acid-analysis  shows  the  presence  of  but  a  very  small  pro- 
portion of  one  or  several  of  the  essential  ingredients,  we  have 


THE  ANALYSIS  OF  VIRGIN  SOILS.  347 

a  valuable  indication  as  to  the  one  of  these  that  will  first  be 
required  to  be  added  when  production  slackens. 

What  arc  "  Adequate  "  Percentages  of  Potash,  Lime,  Phos- 
phoric Acid  and  Nitrogen  ? — It  is  evident  that  a  very  critical 
discussion  of  cultural  experience  can  alone  answer  this  ques- 
tion ;  and  at  first  sight  such  experience  often  appears  very  con- 
tradictory when  compared  with  the  results  of  analysis. 

One  of  the  chief  causes  of  such  apparent  discrepancies  is  readily  in- 
telligible when  we  consider  the  differences  in  root-development  of  the 
same  plant  in  different  soils.  In  "light"  or  sandy  lands  the  roots  may 
penetrate  to  several  times  the  depth  attained  by  them  in  heavy  clay 
soils.  Having  thus  within  their  reach  a  soil-mass  several  times  larger, 
and  aerated  to  a  much  greater  depth,  it  is  but  reasonable  to  expect  that 
in  deep,  sandy  lands  plants  would  do  equally  well  with  correspondingly 
smaller  percentages  of  plant-food  than  would  suffice  in  clay  soils,  in 
which  the  root-range  is  very  much  more  restricted.  The  well-known 
fact  that  the  production  of  heavy  clay  lands  may  be  increased  by  their 
intermixture  with  mere  sand,  adding  nothing  to  their  store  of  plant- 
food,  emphasizes  this  expectation  and  elevates  it  into  a  maxim.  On 
this  ground  alone,  therefore,  it  is  evident  that  the  mere  consideration 
of  plant-food  percentages  found,  can  be  a  true  measure  of  productive- 
ness only  in  the  case  of  virgin  soils  with  high  percentages. 

Soil  Dilution  Experiments. — The  extent  to  which  dilution 
with  mere  "  lightening  "  materials  can  be  carried  without  im- 
pairing production,  can  of  course  be  determined  for  concrete 
cases  only;  but  the  following  experiment  made  at  the  Cali- 
fornia Station  is  a  case  in  point: 

One  kilogram  of  the  heavy  but  highly  productive  black  clay 
soil  of  the  experimental  grounds  of  the  University  of  Cali- 
fornia was  used  in  each  of  five  experimental  cultures,  each 
made  in  duplicate,  in  cylindrical  vessels  of  zinc-covered  (  "  gal- 
vanized ")  sheet  iron,  all  proportioned  alike  in  height  and 
diameter,  but  containing  respectively  one.  two.  four,  five  and 
six  volumes  of  total  soil.  Tn  the  snrillest  was  placed  one  kilo- 
gram of  the  undiluted,  original  soil,  in  the  others  successively 
the  same  amount  of  the  soil  thoroughly  mixed  with  one,  three, 
four,  and  five  volumes  of  a  dune  sand  fully  extracted  with 
chlorhydric  acid,  and  washed  with  distilled  water.  The  water- 


348 


SOILS. 


capacity  of  each  of  the  mixtures  was  determined  and  the  earth 
in  the  pots  kept  at  the  point  of  half-saturation  generally  ad- 
mitted to  be  the  optimum  (best  condition)  for  plant  growth. 
Each  pot  was  sown  with  ten  seeds  of  white  mustard,  subse- 
quently reduced  to  five  plants  selected  for  their  vigor. 

The  ("  galvanized  ")  vegetation  pots  were  made  as  nearly 
as  possible  of  similar  proportions  in  depth  and  width  for  each 
dilution,  so  as  to  give  opportunity  for  the  proportional  develop- 
ment of  the  root  systems.  The  photographs  show  the  latter 
as  nearly  as  practicable  in  their  natural  form,  restored  after 
washing  off  the  adherent  soil  It  was  of  course  extremely  dif- 


FIG.  55. — Same,  diluted  i  to  3. 

DEVELOPMENT  OF   ROOTS  OK  WHITE   MUSTARD  IN   CLAY  SOIL,   DILUTED  WITH 
VARIOUS   PROPORTIONS   OK    PURK    SAND. 


THE  ANALYSIS  OF  VIRGIN  SOILS. 


349 


ficult  to  preserve  intact  the  extreme  circumferential  rootlets 
and  hairs;  yet  the  general  development  is  correctly  shown. 


350 


SOILS. 


FIG.  58. — Soil -dilution  Experiment:   Photograph  showing  Mature  Plants. 

The  following  table  shows  the  percentage  composition  of 
the  original  as  well  as.  the  diluted  soils,  while  the  photographs 
show  the  development  of  the  plants  in  their  successive  stages, 

COMPOSITION'   OF    BLACK    ADOBE    AND    SAND    DILUTION'S. 


Chemical  analysis  of  fine  earth. 

Original 
soil. 
I  :o 

DILUTIONS. 
I  :  I          1:3          i:4          1=5 

Insoluble  matter     

54-50 
19.00 

•73 
.20 

i-'5 
i.  08 
.04 
8.43 
7.92 
.19 
.04 

77-25 
9oO 
•30 
.10 

•57 
•54 

.02 
4.22 

3-9" 

.10 
.02 

88.62 

4-75 
.18 

-05 
.29 

.27 

.01 
2.1  I 
1.98 

•05 
.01 

9O.OO 
3-80 

•15 
.04 

•23 
.22 
O.I 
1.68 
1.58 
.04 

.01 

92.42 
3-17 

.12 

•03 
.19 
.18 
.OI 
1.40 
1.32 

-03 
.OI 

Soluble  silica  

Potash  (K2O)  

Soda  (NasO)  

Lime  (CaO)  

Magnesia  MgO)  

Br.  ox.  of  Manganese  (Mn3O4)  
Peroxid  of  Iron  (FeaOs1     .            .... 

Alumina  (AUOi)  

Phosphoric  acid  (PaO5)  

Sulfuric  acid  (SO,;....           

Carbonic  acid  (CO2)  

Water  and  organic  matter  

6-54 
1.18 

3-27 
.09 

1.64 
.04 

1.31 

.03 

1.09 

•03 

Loss  in  analysis  

Total  

100.00 

I.2I 

•94 
18.58 
.203 

100.00 

.60 

-47 
18.58 
.10 

IOO.OO 

•30 

.21 
18.50 
•05 

IOO.OO 

.24 
.19 
18.58 
.04 

IOO.OO 

.20 
.16 
18.58 
•034 

Humus  

Ash  

"        Nitrogen,  p.  cent,  in  Humus 
"               "          p.  cent,  in  soil  

THE  ANALYSIS  OF  VIRGIN  SOILS. 


351 


so  far  as  these  could  be  observed;  the  continued  attacks  of 
mildew  and  plant  lice  preventing  full  maturity  being  attained. 

The  restricted  volume  of  soil  occupied  by  the  roots  in  the  undiluted 
adobe  soil,  together  with  the  very  abundant  development  of  root-hairs, 
is  very  striking.  A  marked  change  in  these  respects  is  manifest  in  the 
first  dilution,  and  increasingly  so  as  dilution  increases ;  the  paucity  of 
root-hairs  is  very  marked  in  the  last  (greatest)  dilution,  in  which,  as 
the  photograph  of  the  plants  shows,  the  development  was  decidedly 
behind  that  in  the  pot  containing  dilution  i  :  4.  The  latter  in  fact 
showed  the  best  development  not  only  in  this  case,  but  in  two  other 
series  of  tests  conducted  at  the  same  and  subsequent  times  ;  and  strangely 
enough,  also  in  the  pulverulent,  "  sandy  loam "-  soil  of  the  southern 
California  substation  tract.  In  the  latter  series,  which  for  lack  of  space 
cannot  be  figured  here,  the  main  difference  was  that  in  the  undiluted 
soil  the  roots  filled  the  entire  soil  mass,  instead  of  remaining  near  the 
surface,  as  in  the  pure  adobe.  It  is  possible  that  the  latter  was  too  wet 
when  given  the  full  half  of  its  water-capacity,  although,  as  the  figures 
show,  the  water  was  slowly  introduced  from  below  by  means  of  glass 
tubes,  ending  within  a  shield  to  prevent  puddling. 

Limitation  of  Root  Action. — These  results,  representing  five 
soils  of  different  percentage-composition  and  physical  char- 
acter, hut  identical  chemical  composition  and  ratios  between 
the  several  ingredients,  and  similarly  acted  upon  by  the  atmos- 
pheric agencies  in  the  past,  illustrate  strikingly  the  impossi- 
bility of  judging  correctly  of  a  soil's  productiveness  from  per- 
centages of  chemical  ingredients  alone.  It  is  clear  that  the 
physical  characters  of  the  land  as  well  as  its  depth,  must  be 
essentially  taken  into  account.  Hut  there  is  obviously  a  cer- 
tain limit  beyond  which  greater  perviousness  and  root-penetra- 
tion cannot  make  up  for  deficiency  in  the  absolute  amounts  of 
plant-food  within  possible  reach  of  the  plant;  for  in  the  case  of 
excessive  dilution  these  are  rendered  partially  inaccessible 
within  the  time-limits  of  a  season's  growth. 

It  is  hardly  necessary  to  say  that  these  experiments  require 
repetition  with  the  aid  of  the  experience  acquired  in  these  first 
trials,  not  only  in  the  laboratory  but  also  in  the  field.  Tt  will 
be  especially  interesting  to  compare  with  the  results  obtained 
in  these  strongly  calcareous  soils,  the  effects  of  dilution  in  such 


352 


SOILS. 


soils  as  those  of  Florida,  mentioned  below ;  the  probability  be- 
ing that  where  lime  is  naturally  deficient,  the  effects  of  dilu- 
tion will  be  much  more  pronounced  in  diminishing  production, 
because  of  the  absence  of  the  previous  favorable  action  of  lime 
upon  the  availability  of  the  soil-ingredients. 

Lowest  Limit  of  Plant-food  Percentages  and  Productive- 
ness found  in  Virgin  Soils. — The  subjoined  table  shows  some 
of  the  very  low  plant-food  percentages  found  in  natural  soils, 
all  being  of  a  sandy  character : 


MISSISSIPPI  SOILS. 

FLORIDA  SOILS. 

Homo- 
chitto 
Bottom. 

Shell 
Ham- 
mock. 

Pine 
Woods. 

Pine 
Flats. 

Pine  Lands. 

First 
Class. 

Second 
Class. 

Number  of  Sample. 

68 

83 

206 

214 

6 

7 

CHEMICAL  ANALYSIS  OF  FINK 
EARTH. 

j  92.16 

•'5 

.12 
.21 

.28 

1.18 

3.o8 
.05 

96.08 

.05 
.06 
.10 

.12 
•t>5 
•52 
.46 
.IO 

Trace 

93-23 
26 
07 

12 

18 
15 
'  25 
236 

03 

02 

95-59 
.06 
•°5 

.02 
.07 
.05 
.46 
.85 
.02 

Trace 

94.46 

1.67 

•>9 
.04 
.07 
.04 
.06 
-32 
•92 
.11 
.09 

9S:S}*s« 

.12 
.06 
.06 
.04 
.05 
.22 

•47 
.OQ 
.06 

Potash  (  K2O)  

Soda   (Na2O)  

Lime  (CaO)  

Br.  ox.  of  Manganese  (Mn3O4). 
Peroxid  of  Iron  (Fe2O3)  

Phosphoric  acid  (  PsOs  )  

Water  and  organic  mailer  
Total  

2.70 

3.02 

2-33 

2.28 

1.88 

1.81 

100.19 

100.56 

IOO.OO 

99-45 

99.85 

99-49 

The  average  of  plant-food  percentages  in  all  these  soils  is 
quite  low,  and  at  first  sight  there  seems  to  be  little  choice  be- 
tween them.  Yet  two  of  them — Xos.  68  and  88,  from  Missis- 
sippi— are  not  only  quite  productive  at  the  outset,  but  also 
fairly  durable.  This  becomes  measurably  intelligible  when  it 
is  known  that  both  are  of  great  depth,  and  so  well  drained  that 
roots  can  descend  for  many  feet ;  while  the  composition  of  the 
soil-material  is  almost  identical  for  three  or  four  feet.  On  the 
other  hand,  both  Nos.  206  and  214  are  quite  shallow,  being  un- 
derlaid by  sand  almost  devoid  of  plant-food  at  about  two  feet. 
In  addition,  both  have  extremely  low  percentages  of  phos- 
phoric acid;  while  the  rest  show  near  .10%  of  that  ingredient, 
an  amount  which,  as  will  be  seen  hereafter,  is  considerably 


THE  ANALYSIS  OF  VIRGIN  SOILS.  353 

above  the  recognized  limit  of  deficiency.  The  two  Florida 
soils  however  bear  only  pine;  they  are  underlaid  by  almost 
clean  sand  at  two  or  three  feet,  and  are  therefore  quickly  ex- 
hausted. It  will  also  be  noted  that  their  lime-percentage  is 
only  about  half  of  that  of  the  two  first-named  Mississippi 
soils,  both  of  which  bear  a  strong  growth  of  deciduous  timber 
trees,  grape  vines,  and  other  vegetation  indicating  the  presence 
of  lime  carbonate. 

It  is  noteworthy,  also,  that  the  popular  classification  of  the 
two  Florida  soils  corresponds  exactly  with  the  differences  in 
the  percentages  of  plant-food;  those  in  the  "  second-class  "  soil 
being  uniformly  lower  than  those  in  the  one  designated  as  first- 
class.  This  indicates,  again,  that  as  between  soils  of  similar 
character  and  origin,  the  production  and  durability  arc  sensibly 
proportional  to  the  plant-food  percentages  when  the  latter  fall 
below  a  certain  limit ;  a  point  more  fully  illustrated  farther  on. 

In  the  light  of  the  above  experiment  and  tables,  it  becomes 
pertinent  to  consider  what  arc  the  lowest  percentage  limits  of 
each  of  the  more  important  plant-food  ingredients  compatible 
with  profitable  production. 

LIMITS  OF  ADEQUACY  OF  THE  SEVERAL  PLANT-FOODS  IN  VIRGIN 

SOILS. 

It  is  obvious  that  the  lower  limits  of  adequacy  of  the  critical 
plant-food  ingredients  are  best  ascertained  in  the  case  of  virgin 
soils  containing  very  small  amounts  of  some  one  ingredient, 
while  fairly  or  fully  supplied  with  the  rest.  In  such  cases, 
which  are  not  at  all  infrequent,  the  use  of  the  deficient  ingre- 
dient as  a  fertilizer  should  produce  a  very  marked  effect  so 
soon  as  the  first  (lush  of  production  (always  noted  in  fresh 
soil)  is  over.  This  first  productiveness  may.  even  in  poor 
lands,  range  from  one  to  three  years,  when  there  is  a  sudden 
decline. 

Lime  a  Dominant  Factor. — When  we  investigate  the  cases  of 
such  lands,  it  soon  becomes  apparent  that  besides  the  low  per- 
centage of  any  one  ingredient,  the  proportions  of  others  pres- 
ent require  consideration.  Among  these,  lime  in  the  form  of 
carbonate  stands  foremost.  Its  presence  exerts  a  dominant 
and  beneficial  influence  in  many  respects,  as  is  readily  apparent 
23 


354  SOILS. 

from  the  prompt  change  in  vegetation  whenever  it  is  intro- 
duced into  soils  deficient  in  it.  In  discussing  the  results  of 
soil  analysis,  its  consideration  is  of  first  importance  in  fore- 
casting correctly  the  adequacy  or  inadequacy  of  other  soil  in- 
gredients ('see  chapter  20,  page  379).  For  in  general,  we  find 
that  lower  percentages  of  potash,  phosphoric  acid  and  nitrogen 
are  adequate,  when  a  large  proportion  of  lime  carbonate  is 
present. — This  has  already  been  referred  to  in  connection  with 
the  table  of  soils  of  low  percentages,  given  above.  In  the  in- 
terpretation of  results  obtained  by  analysis  this  point  must  al- 
ways be  kept  in  view;  and  in  the  numerical  statements  made 
below,  it  must  be  understood  that  they  refer  to  virgin  soils 
sufficiently  supplied  with  lime  to  assure  a  constant  excess  of 
lime  carbonate,  maintaining  the  conditions  of  nitrification  and 
insuring  the  absence  of  acidity.  (See  chapter  9,  page  146). 
Potash. — In  respect  to  potash,  the  writer  was  led  by  his 
early  investigations  in  the  State  of  Mississippi  to  conclude  that 
less  than  one- fourth  of  one  per  cent  (.25)  of  potash  consti- 
tuted a  deficiency  likely  to  call  for  early  fertilization  with 
potash  salts;  while  as  much  as  .45%  of  the  same  seemed  to 
cause  the  land  to  respond  but  feebly  to  such  fertilization.  He 
has  not  found  it  necessary  to  revise  materially  that  early  con- 
clusion, whether  from  his  own  work  or  from  that  of  others. 
Within  the  last  decade,  Prof.  Liebscher  of  Gottingen  1  has  ar- 
rived at  this  identical  figure  from  analyses  made  of  soils  upon 
which  he  had  conducted  a  seven-year  series  of  fertilizer  tests; 
he  having  found  that  potash  fertilization  produced  no  sensible, 
or  at  least  no  paying  results  on  land  giving  that  figure, 
and  otherwise  well  provided  with  plant-food.  The  different 
(lower)  figures  given  by  Schloesing,  Risler  and  other  French 
chemists  in  discussing  the  soils  of  France,  are  doubtless  due  to 
the  weak  acid  and  short  period  of  digestion  employed  in  the 
analysis;  an  unfortunate  discrepancy  of  methods  which  pre- 
cludes any  direct  comparison  of  results. 

These  figures  apply  both  to  the  arid  and  the  humid  regions  in  the 
temperate  zones.  In  the  tropics  we  find  very  much  lower  percentages 
quoted  as  adequate ;  thus  in  the  laterite  soils  of  India  and  Samoa, 

1  Untersuchungen  uber  die  Kestimmungdes  Diingerbediirfnisses  cler  Ackerboden 
und  Kulturpflanzen,  von  G.  Liebscher;  Journal  fur  Landwirtschaft  43  <  1895), 
Nos.  i  &  2,  pp.  48-216. 


THE  ANALYSIS  OF  VIRGIN  SOILS.  355 

according  to  Wohltmann,  in  the  soils  of  Jamaica  according  to  Fawcett, 
and  in  those  of  Madagascar  according  to  Miintz  and  Rousseaux.1 
There,  potash-percentages  over  .10%  seem  to  be  high,  and  in  Mada- 
gascar some  lands  in  fair  production  range  as  low  as  .01%.  The  soil- 
extractions  have  however  in  these  cases  been  made  with  a  weaker  acid 
than  above  specified,  so  that  some  increase  of  the  figures  (perhaps  33 
to  50%)  vvill  have  to  be  allowed  for.  But  even  then  there  can  be  no 
question  that  a  far  less  amount  of  potash,  as  determined  by  acid-ex- 
.  traction,  is  found  sufficient  for  crop  production  in  the  tropics  ;  doubtless 
because  of  the  very  intense  decomposing  (  "  fallowing"  )  effect  of  the 
continuous  heat  and  moisture,  tending  also  to  a  rapid  decomposition 
of  organic  matter  and  a  proportionally  rapid  formation  of  carbonic  and 
nitric  acids.  Such  soils  are  of  course  constantly  kept  in  a  leached  con- 
dition, as  a  result  of  the  heavy  and  continuous  rainfall. 

Phosplwric  Acid. — As  regards  the  lower  limit  of  adequacy 
of  phosphoric  acid,  there  is  a  remarkable  agreement  in  the  in- 
vestigations made  everywhere.  It  was  placed  at  .05%  by  the 
writer  as  long  ago  as  1860,  as  the  result  of  investigations  made 
in  the  State  of  Mississippi ;  and  the  same  figure  has  since  been 
arrived  at  independently  by  agricultural  chemists  in  France, 
Russia,  Germany  and  England.  The  cause  of  this  remarkable 
agreement  is  undoubtedly  the  readiness  with  which  the  phos- 
phates that  come  under  consideration  at  all  for  the  nutrition 
of  plants,  are  dissolved  by  almost  any  acid  treatment  likely 
to  be  used  in  soil  analysis.  Almost  the  same  agreement  exists 
in  regard  to  the  "adequacy"  of  .\''/<  of  P-Or> ;  while  all  soils 
showing  percentages  between  .1  and  .05^  are  considered  weak 
on  this  side,  and  liable  to  need  phosphate  fertilization  soon. 
One-fourth  of  one  per  cent  is  an  unusually  high  percentage 
in  most  countries;  .3Or/r  and  over  is  exceptional  in  non-fer- 
ruginous soils.  But  as  stated  on  a  previous  page,  a  high  per- 
centage of  lime  carbonate  may  offset  a  smaller  percentage  of 
phosphoric  acid,  apparently  by  bringing  about  greater  avail- 
ability; and  a  similar  effect  seems  to  result  from  the  presence 
of  a  large  supply  of  humus. 

On  the  other  hand,  very  large  ]>ercentages  of  finely  divided 
ferric  hydrate  may,  especially  in  the  absence  of  lime  carbonate, 

1  La  J 'aleur  Agricole  Jes  Tfrres  Je  Madagascar.  Ann.de  la  Science  Agrono 
•snique,  2'me  serie,  tome  I,  1901. 


356 


SOILS. 


render  even  large  supplies  of  phosphoric  acid  inert  and  use- 
less, by  the  formation  of  the  totally  insoluble  ferric  phosphate. 
Aluminic  hydrate  probably  acts  in  a  similar  manner.  The 
following  table  gives  examples  in  point,  as  regards  ferric 
hydrate. 

HAWAIIAN  SOILS  SHOWING  HIGH  CONTENTS  OF  FERRIC  OXID. 
(Kept.  Cal.  Exp.  Sta.  1894-5,  page  27.) 


Oahu. 

Hawaii. 

NUMBER  OF  SAMPLE. 

No.  21. 

No.  22. 

No.  24. 

No.  26. 

No.  27. 

5.00 
95.00 

21.07 
2.68 

•44 
.25 

'.60 

.07 
30.10 
14-38 
•97 
•29 

Coarse  Materials^  o  55mm  

2.OO 

98.00 

15.84 

14.07 

•45 
.14 
.26 
•65 
•05 
39-05 
14.61 

•'9 
•03 

2.50 

97-5° 

14.49 

30-37 
.26 
.08 
1.04 
.80 

«S 

18.29 

•32 
.09 

4.00 
96.00 

26.99 
10.26 
.40 
.26 

$ 

.21 
ig.IO 
21.41 
.64 
•32 

3.00 
97.00 

28.66 

7^5 
.61 

•17 
.68 
1.04 
.20 
18.23 
20.18 
.70 

.21 

Fine  Earth  

CHEMICAL  ANALYSIS    OF  FINE 
EARTH. 

Soluble  Silica  

Potash  (K2O)  

Soda  (Na2O)  

Lime  (CaO)   

Magnesia  (MgO)  

Br.  ox.  of  Manganese  (Mn3O4).. 
Peroxid  of  Iron  (  FetOa).  .  ..,  . 

Alumina  (  AlzOs)  

Phosphoric  acid  (  PsO6)  

Sulf  uric  acid  (SOa)...  

Carbonic  acid  (CO2)  

Water  and  organic  matter.  

14.18 

14-59 

18.60 

21.65 

28.60 

Total  

99-52 

3-35 
3.12 

3-3o 

.112 

.no 

.OO4 
.IOO 

•43° 
18.50 

100.04 
3-24 

2.22 
9.800 

•3!4 
.166 
.O2O 
.320 
•350 
21.25 

99.67 

4.84 
2.76 
2.800 

•134 

.580 

.035 
.640 
i.  600 
23.07 

99.6l 

5-43 
3-5° 
3.100 
.168 
.500 

•037 
.700 
1.280 
23-14 

99-73 

9-95 
6.70 
1.71 
•  17 

.025 
.970 

23.81 

Humus  

"     Ash  

"     Nitrogen,  p.  c.  in  Humus.. 
"         ,  p.  c.  in  soil  

Phosph.  acid  in  humus  ash  

Soluble  in  2  °'0  Citric  acid.  .  .  . 
in  Nitric  acid,  1.20  sp.  g.  .  .  .  . 
in  Chlorhyclric  acid  1.115  SP-  g 
Hygroscopic  moisture  1  5°  C  

Unavailability  of  Ferric  Phosphate. — It  will  be  noted  that  in  the  soils 
from  Oahu  with  an  overwhelming  amount  of  ferric  oxid  (mostly  in  the 
form  of  hydrate  or  rust)  the  citric  acid  has  taken  up  only  an  insigni- 
ficant amount  of  phosphoric  acid ;  nitric  acid  took  up  40  to  50  times  as 
much,  and  chlorhydric  doubled  even  this.  In  the  much  less  ferruginous 
Hawaiian  soils,  though  containing  more  alumina,  the  citric  acid  ex- 
tracted nearly  ten  times  as  much ;  proving  that  it  is  chiefly  ferric  oxid, 
and  not  the  alumina  as  has  been  supposed,  that  causes  the  insolubility 


THE  ANALYSIS  OF  VIRGIN  SOILS.  357 

of  phosphoric  acid  in  soils  and  doubtless  also  in  fertilizers.  The  very 
unusually  high  content  of  phosphoric  acid  in  the  Hawaiian  soils,  ex- 
ceeding all  others  on  record,  so  far  as  known  to  the  writer,  emphasize 
the  effects  of  ferric  hydrate  upon  soluble  phosphates ;  while  the  fact 
that  these  very  soils  are  greatly  benefited  by  the  use  of  phosphate  fer- 
tilizers, proves  that  the  Dyer  (citric  acid)  method  for  the  determination 
of  available  phosphoric  acid  which  in  soils  Nos.  21  to  26  yielded  results 
largely  in  excess  of  the  established  limit  in  European  soils,  cannot  be 
successfully  applied  to  these  highly  ferruginous  soils.  It  should  also  be 
noted  that  the  amounts  of  phosphoric  acid  found  in  the  humus  extracted 
by  the  Grandeau  method  is  in  the  first  two  Hawaiian  soils  over  ten 
times  the  amount  extracted  by  citric  acid,  but  that  while  they  rise  and 
fall  together,  no  definite  quantitative  ratio  exists  between  the  two. 

It  is  obvious  that  in  such  soils,  fertilization  with  water-solu- 
ble phosphates  would  be  likely  to  result  in  the  quick  partial 
withdrawal  of  the  same  from  useful  action,  and  that  any  ex- 
cess not  promptly  taken  up  by  the  crop,  is  likely  to  become 
inert  and  useless.  It  will  evidently  be  desirable  to  use  the 
phosphates  in  the  form  of  bone-meal  or  basic  slag"  ( Thomas 
Phosphate),  which  because  of  their  difficult  solubility  will  be 
acted  upon  but  very  slowly,  if  at  all,  by  the  ferric  and  aluminic 
hydrates. 

Nitrogen. — In  determining  the  nitrogen-content  of  the  soil, 
a  great  variety  of  methods  has  been  followed.  Some  include 
all  that  can  be  obtained  by  the  combustion  of  the  organic  mat- 
ters of  soil  and  from  the  nitrates  present  in  the  same;  while 
others,  the  writer  among  the  number,  believe  that  the  mainly 
important  source  of  nitrogen  to  the  plant  being  the  nitrifica- 
tion of  the  humus-nitrogen,  the  determination  of  the  humus 
by  the  method  of  (Irandeau,  and  of  the  nitrogen  contained  in 
it,  should  be  the  standard  ;  the  unhumiried  vegetable  matter 
being  of  no  definitely  ascertninable  value,  and  the  nitrates 
varying  from  day  to  day  and  being  liable  to  be  lost  by  leach- 
ing at  any  time;  therefore  forming  no  permanent  feature  of  the 
soil.  Considering  the  variety  of  methods,  the  unanimity  with 
which  about  one-tenth  of  one  per  cent  (  .10)  has  been  assumed 
as  the  ordinarily  adequate  percentage  is  remarkable.  In  view 
of  the  extremely  variable  amount  of  nitrogen  in  the  humus 
(ranging  from  1.7  to  nearly  JJ'r),  the  amount  of  the  latter 


358  SOILS. 

cannot,  of  course,  afford  even  an  approximation  to  the  nitn> 
gen-content ;  except  that  as  in  the  humid  region,  the  nitrogen- 
percentage,  is  not  known  to  exceed  about  5  or  5.5%,  an  ap- 
proximate estimate  can  be  made  on  that  basis.  In  the  arid 
region,  according  to  location,  the  nitrogen-percentage  may  be 
from  three  to  six  times  greater  for  a  similar  amount  of  humus. 
(See  chap.  8,  p.  135).  In  the  writer's  experience,  a  nitro- 
gen-percentage of.i%  in  the  arid  region  is  a  very  satisfactory 
figure,  indicating  that  the  need  of  nitrogen-fertilization  is  not 
likely  to  arise  for  a  number  of  years. 

Nitrification  of  the  Organic  Matter  of  the  Soil. — In  order  to  test  the 
question  whether  or  not  the  nitrogen  of  the  unhumified  debris  existing 
in  surface  soils  is  directly  nitrifiable,  the  writer  selected  a  soil  which  in 
its  natural  condition  sustains  intense  nitrification,  so  that  at  some  points 
it  contains  as  much  as  1200  pounds  of  sodic  nitrate  per  acre.  The 
composition  of  this  soil,  representing  the  land  of  the  "ten-acre  tract" 
of  the  southern  California  sub-station,  is  as  follows  : 

SOIL  FROM   "TEN-ACRE   TRACT,"  SOUTHERN   CALIFORNIA   SUB-STATION,   NO.  1284. 

Coarse  Materials  >  o.55mm i.oo 

Fine  Earth 99.00 

100.00 

CHEMICAL   ANALYSIS    OF   FINE    EARTH. 

Insoluble  matter 62.62  \ 

Soluble  silica ...  8.30  j  7°'92 

Potash  (K2O) .95 

Soda  (Na2O) .50 

Lime  (CaO) 5.07 

Magnesia  (MgO) ...    .84 

Br.  ox.  of  Manganese  (MnsO*) .06 

Peroxid  of  Iron  (FeaOa) 6.43 

Alumina  (A1,O3) 3.88 

Phosphoric  acid  (PaOs) .21 

Sulfuric  acid  (SO3)   06 

Carbonic  acid  (C  O2) 3.66 

Water  and  organic  matter 6.02 

Total 99-7° 

Water-soluble  matter,  percent .137 

Sodic  nitrate,  per  cent .020 

Humus 1 .99 

"         Ash 1.13 

"         Nitrogen,  per  cent,  in  Humus 10.30 

"                "       ,  per  cent,  in  soil .203 

Total  Nitrogen  in  soil 330 

"                       in  unhumified  matter .127 

Available  Potash j    citric     ) 

Available  Phosphoric  acid  \  method  ) 

Hygroscopic  Moisture 5.81 

absorbed  at 15°  C. 


THE  ANALYSIS  OF  VIRGIN  SOILS.  359 

It  will  1)6  noticed  that  this  is  a  rather  strongly  calcareous  soil,  (nearly 
9%  of  calcic  carbonate),  slightly  impregnated  with  alkali,  of  which  aboul 
one-ninth  is  saltpeter.  One  portion  of  this  soil  was  thoroughly  leached 
with  distilled  water  until  not  a  trace  of  nitrates  could  be  detected  in  the 
leachings.  Another  portion  was  treated  for  the  removal  of  humus 
according  to  the  Grandeau  method  (see  chapter  8,  page  132);  the  ex- 
tracted soil  showed  under  the  microscope  an  abundance  of  vegetable 
debris,  some  slightly  browned  as  from  incipient  humification. 

The  calcic  and  magnesic  carbonates  withdrawn  in  the  humus-extrac- 
tion were  then  restored  to  the  soil  in  the  form  of  finely  divided  pre- 
cipitates and  thoroughly  mixed  in,  first  in  the  dry  and  then  in  the  wet 
condition ;  the  extracted  soil  being  repeatedly  wetted  with  turbid  water 
from  the  leached  soil,  in  order  to  replace  and  reinfect  it  with  the  nitri- 
fying bacteria.  Both  soils  were  then  spread  out  in  flat  glass  dishes  and 
placed  in  a  wooden  box  containing  also  a  similar  flat  dish  with  distilled 
water,  upon  which  played  the  draught  from  the  inlet  pipe  opening  into 
the  outer  air,  with  outlet-holes  in  the  cover  at  the  opposite  end;  thus 
keeping  the  air  within  fairly  moist.  In  addition,  the  soils  themselves 
were  moistened  with  distilled  water  every  three  days  and  restored  to  a 
loose  condition  by  stirring.  The  whole  was  placed  so  as  to  maintain, 
during  the  greater  part  of  the  24  hours,  a  temperature  of  from  30  to 
35  degrees  C.  At  intervals  the  samples  of  both  soils  were  leached  and 
color-titrated  for  their  nitrate  content  by  the  picric-acid  test.  The 
results,  calculated  as  sodic  nitrate,  during  two  years  were  as  follows : 


Nitrate  formed  during Four  months.    Twelve  months.  Two  years. 


I. cached  natural  soil. 
Extracted  soil 


.012 


\ 


one. 


.0420 
.0030 


.061 
.0042 


It  will  be  noted  that  in  the  course  of  four  months,  nitrification  had 
not  sensibly  set  in  in  the  extracted  soil  ;  while  in  the  leached  natural 
soil  the  nitrate-content  had  reached  to  three-fifths  the  amount  originally 
present,  and  in  the  course  of  a  year  the  nitrate-content  of  the  latter 
was  more  than  double  that  of  the  original  (unleached)  soil ;  while  that 
in  the  extracted  soil  had  only  reached  one-seventh  of  the  same.  At 
the  end  of  two  years  we  find  a  still  farther  increase  of  nitric  nitrogen  in 
both,  the  ratio  between  the  two  remaining  about  the  same  (i  :  14). 
At  the  same  time  the  ratio  of  increase  attained  at  first  had  materially 
diminished  in  the  water-leached  soil,  probably  on  account  of  the  accumu- 
lation of  the  niter  itself. 


360  SOILS. 

It  thus  appears  that  although  the  nitrogen  of  the  unhumified 
organic  matter  constituted  about  40%  of  the  total  in  the  origi- 
nal soil,  it  would  during  the  entire  year  have  contributed  only 
to  an  insignificant  extent  to  the  available  nitrate-supply ;  while 
the  fully  humified  "  matiere  noire  "  contributed  fourteen  times 
as  much.  During  the  ordinary  growing-season  of  four  or  five 
months  the  unhumified  organic  matter  would  have  yielded 
practically  nothing  to  the  crop. 

Functions  of  the  unhumified  Vegetable  Matter. — The  chief 
utility  of  the  unhumified  matter  in  the  soil  consists  of  course 
in  its  gradual  conversion  into  true  humus,  in  the  course  of 
which  it  evolves  carbonic  gas  to  act  on  the  soil  minerals ;  while 
at  the  same  time  it  helps  to  render  the  soil  more  porous  and 
thus  facilitates  the  action  of  the  aerobic  bacteria,  for  which  it 
serves  as  food.  Hence  the  addition  of  vegetable  matter  to  soils 
not  already  too  "  light  "  is  always  advantageous,  so  long  as 
it  does  not  introduce  injurious,  non-humifiable  ingredients, 
like  turpentine  in  the  sawdust  of  resinous  pines.  But  it  is  al- 
ways advisable  to  first  use  such  matter  as  litter  for  stock,  in 
order  to  better  prepare  it  for  the  processes  of  humification, 
under  the  influence  of  ammonical  fermentation,  such  as  occurs 
in  the  decay  of  green  plants  or  animal  matter.  A  portion  of 
the  ash  ingredients  also  is  quickly  utilized  by  solution  in  the 
soil-water. 

Matiere  Noire  the  Only  Guide. — According  to  these  results 
it  is  clear  that  in  order  to  gain  any  tangible  indications  with  re- 
spect to  crop-bearing,  it  is  the  nitrogen  in  the  humus  proper, 
the  matiere  noire  only,  that  should  serve  as  the  basis ;  and  that 
as  a  current  source  of  nitrogen  to  the  plant,  the  unhumified 
matter  is  hardly  entitled  to  more  consideration  than  the  "  in- 
soluble silicates."  For,  the  favorable  conditions  for  nitrifica- 
tion under  which  the  above  experiment  was  conducted,  will 
very  rarely  be  even  approached  under  field  conditions. 

What  are  the  Adequate  Nitrogen  Percentages  in  the  Humus  f 
The  nitrification  of  the  matiere  noire  being,  apparently,  the 
main  source  of  plant-nutrition  with  that  element  under  ordin- 
ary conditions,  the  question  naturally  arises  as  to  what  may  be 
considered  an  adequate  nitrogen-content  of  that  substance,  so 
as  to  permit  a  full  supply  of  nitrates  to  the  crop. 


THE  ANALYSIS  OF  VIRGIN  SOILS. 


361 


The  data  extant  on  this  subject  are  rather  scanty,  and  thus 
far  have  all  been  obtained  at  the  California  Experiment  Sta- 
cion.1  But  they  seem  to  be  very  cogent  in  proving  that  the 
growth  of  crops  removed  from  the  soil  causes  a  rapid  deple- 
tion of  the  nitrogen  in  the  humus-substance,  and  that  so  soon 
as  the  nitrogen-percentage  in  the  same  falls  below  a  certain 
point,  the  soil  becomes  "  nitrogen-hungry;  "  so  that  the  applica- 
tion of  nitrogenous  fertilizers  is  needed  and  is  very  effective. 
The  data  in  the  table  below,  as  well  as  the  figure  of  a  culture 
experiment  (  Xo.  52  below),  illustrate  this  point. 

ADEQUACY   AND    INADEQUACY   OK   XITKOUKX    CONTEXTS   OK    HTMt'S. 


Collec- 

Per cent. 

Per  cent. 

Per  cent. 

tion 

Kind  of 

Locality. 

Num- 

Soil. 

Humus  in 

Nitrogen 

Nitrogen 

ber. 

Soil. 

in  Humus- 

in  Soil.1 

6 

Black  Adobe. 

Near  Stockton,  San  Joaquin 

Co.,  Cal  

I.Os 

iS.66 

.196 

1679 

do 

Virgin        Soil,      University 

(  1  rounds,  Berkeley  

I   °O 

1  8  sS 

.''O7 

1842 

do 

Ramie  plot,  Univ.  (1  rounds, 

10  years  cultivated  

i.  So 

J.I7 

.07  ? 

1841 

do 

(irass    plot,  Univ.  Grounds, 

10  years  cultivated  

i  6; 

.056 

-9 

Dark  loam. 

Sugarcane  land,    Maui,    If. 

T  

10  90 

~7 

1  )ark  loam. 

(iiiava-land  hills,  near  llilo, 

0-     J5 

Hawaii  Isl'd  

O  ON 

I   ~  I 

I  ~O 

Nos.  6  and  1679  show  the  usual  humus-  and  nitrogen-percentages  in 
the  "black  adobe"  or  "prairie"  soils  of  California.  Xos.  1842  and 
1-^41  represent  the  same  soil  as  1679,  upon  which,  however,  ramie  and 
ray  grass  had  respectively  been  growing,  without  fertilization,  for  about 
ten  years  ;  showing  that  while  the  humus-content  of  the  soil  has  /;/r/vw.\vv/, 
the  nitrogen-content  of  the  hinnns  //</.»•  dt-crcascJ  in  the  case  of  ramie  by 
72.78^',  in  that  of  the  grass  by  76.78',,'  ;  reducing  the  land  to  figures 
commonly  found  in  the  humid  region.  In  the  case  of  the  ramie,  the 
partial  return  through  the  leaves  has  resulted  in  a  higher  humus-content, 

1  The  Supply  ef  Si'il  A'r/nw/i,  Krp.  Cal.  l-'.xpt.  Station,  iS<)j-<r,.  page  6S  ;  ibid., 
€894-95,  page  28;  7"ic-  Ri-ci'^iiitii'H  ,>/' A'itr; ;;•',-//  Hnn^riucss in  .S'i'/.V,  in  Mull.  47,  l>iv. 
of  Chemistry,  U.S.  Department  of  Agriculture,  i8<);;  I.aiuUv.  Pressc,  Xo.  ;  5,  July 
188^.  See  also  for  detailed  data  chapter  8,  page  13;. 

-  Calculated  upon  the  true  humus  substance  imatiere  noire),  //<'/  by  detei  mining 
total  (incl.  unhumified)  nitrogen  in  the  soil. 


362 


SOILS. 


together  with  higher  nitrogen-percentage,  than  in  the  case  of  the  grass. 
which  in  the  several  cuttings  annually  made,  caused  a  greater  depletion 
in  nitrogen  and  a  smaller  accession  of  humus.  The  grass  was  very 
weak  in  its  growth  and  partially  dying  out. 

No.  29,  the  sugar-cane  land  from  Maui,  was  still  in  fair  production, 
but  beginning  to  weaken  as  against  its  first  production.  No.  27, 
the  guava  land  from  Hawaii,  originally  bore  a  luxuriant  cover  of 
Avild  guava,  but  after  bearing  one  fair  crop  of  seed-cane  and  one  of 
ratoons,  the  cane  planted  on  it  "  spindled  up  "  and  died  so  soon  as  the 
seed-cane  planted  was  exhausted.  Both  the  island  soils,  originally 
derived  from  the  weathering  of  the  black  basaltic  lavas  of  the  region, 
were  well  supplied  with  mineral  plant-food  (see  above,  page  356),  and 
the  humus-content  in  both  was  exceptionally  high ;  and  neither  was  in 
an  acid  condition.  The  difference  in  their  nitrogen-content,  both  in 
the  totals  and  in  the  humus  itself,  suggested  that  notwithstanding  the 
relatively  high  total  of  nitrogen  in  No.  27,  it  might  be  nitrogen-hungry, 
in  view  of  the  low  percentage  of  the  nitrogen  in  the  humus. 

Confirmatory  Experiment. — A  pot-culture  with  wheat,  the 
results  of  which  are  shown  in  the  figure  below,  fully  confirm 


FIG.  59. — Growth  of  Wheat  on  Guava  Soil  from  Hawaii  Island. 

this  suspicion.     One  kilogram  of  soil  was  used  in  each  of  two 
pots,  one  being  fertilized  with  half  a  gram  of  Chile  saltpeter. 


THE  ANALYSIS  OF  VIRGIN  SOILS.  363 

The  experiment  could  not  be  carried  to  full  completion  on  ac- 
count of  the  overwhelming  invasion  of  mildew ;  but  the  figures 
speak  for  themselves.  Moreover,  a  field  trial  made  on  the 
island  with  saltpeter,  in  pursuance  of  the  writer's  recommen- 
dation, resulted  in  a  luxuriant  growth  of  the  cane. 

Data  for  Nitrogen-adequacy. — It  appears  from  the  facts 
shown  above,  that  for  the  growth  of  grasses  a  nitrogen-per- 
centage in  the  humus  of  1.7  is  wholly  inadequate,  no  matter 
how  much  humus  may  be  present.  A  percentage  of  3.15  in 
the  Maui  soil,  No.  29.  containing  nearly  1 1  %  of  humus,  gave 
only  a  fair  crop  of  sugar-cane ;  on  the  Berkeley  grass  plot,  with 
3.40%  and  only  1.65  of  total  humus,  the  ray  grass  was  barely 
maintaining  life.  The  ramie,  with  4.1790  of  nitrogen  in  the 
soil-humus,  was  still  doing  fairly  well. 

It  is  doubtless  impossible  to  give  one  and  the  same  absolute 
figure  for  nitrogen-deficiency  for  all  plants  and  soils.  Where 
the  conditions  of  nitrification  are  favorable,  as  in  the  presence 
of  much  of  the  earth  carbonates,  a  smaller  percentage  may 
suffice  for  the  same  plants  that  elsewhere  suffer  ;  and  it  is  highly 
probable  that  different  minima  will  be  found  for  plants  of  dif- 
ferent relationship  and  root-habits.  But  there  is  every  reason 
to  believe  that  in  the  nitrogen-percentage  of  soil-humus,  con- 
sidered in  connection  with  other  chemical  and  physical  condi- 
tions and  soil  derivations,  we  have  a  means  of  ascertaining  the 
needs  of  plants  with  respect  to  nitrogen-fertilization,  if  proper 
study  be  given  to  the  subject.  Broadly  speaking,  it  appears  to 
be  necessary  to  keep  the  nitrogen-percentage  of  soil-humus  near 
4%  to  insure  satisfactory  production. 

It  having  been  suggested  that  the  frequent  and  disastrous 
crop  failures  on  the  noted  tchernoxem  or  black-earth  soils 
of  Russia  might  be  due  in  part  at  least  to  nitrogen-depletion 
of  the  humus,  the  writer  obtained  through  the  courtesy  of 
Prof.  P.  Kossovitch  of  St.  Petersburg  soil  samples  from  the 
center  of  the  Black-earth  region,  both  cultivated  and  unculti- 
vated. These  samples  arc  in  appearance  exactly  like  some  of 
the  dark  alluvial  soils  of  Louisiana  and  California,  and  ap- 
proach them  very  nearly  in  the  essentials  of  composition,  as 
will  be  seen  from  the  table  below : 


364 


SOILS. 

ANALYSES  OF  BLACK  SOILS, 


Tchernozem 
(Russia.) 

Alluvial 
Black  clay  lands. 

Virgin. 

Culti- 
vated. 

Louisiana. 

No.  240. 

California. 
No.  1167. 

Back-land 
Houma. 

Black-land 
Tulare. 

CHEMICAL   ANALYSIS   OF   FINE   EARTH. 

(No  coarse  material  in  soils.) 
Insoluble  matter  ,. 

48.38 
13.21 

.72 
.20 
i-5J 
•73 
•°5 
7.12 

5-22 
.14 
.07 

55-09 
12.28 

•52 

•!3 

l-3i 

•75 
•03 
4.80 

4-73 
•J3 

.08 

19.94 

35-48 
20.76 
1.03 

•'3 

•72 
.88 
.01 
7.10 
J5-45 
•'5 
•25 

18.52 

62.43 
16.99 
1.09 

•77 
1.46 
1.44 
.06 
4.98 
6.87 

.12 

.02 

Potash  (KaO)  

Soda  (NaaO  

Lime  (CaO)  

Magnesia  (MgO)  

Peroxid  of  Iron  (FeaO3).  ,  

Alumina  (  A1»O3)      

Phosphoric  acid  (P,,Os)  

Sulf  uric  acid  (SO)  

Carbonic  acid  (COa)  

\Vater  and  organic  matter  

22.78 

Total  

100.13 

5.II 
1.  80 

4-63 

.27 

.OI4 

.on 

99-79 

5-54 
1.40 
4.22 
.24 

.010 
.008 

12.07 
i7°C 

100.48 

5.07 
•9i 

".08 

18.82 
i3°C 

IOO-59 

i-33 
•36 

.01 

5-38 
i5°C 

Humus  

»         Ash  

"         Nitrogen,  per  cent,  in  Humus.. 
"                 "         per  cent,  in  soil.  .    .. 

Available  Potash  j  citric  acid  ) 

Available  Phosph.  acid     (    method     J 
Hygroscopic  Moisture  

absorbed  at  

It  will  be  seen  that  the  Russian  soil  is  of  high  fertility  ac- 
cording to  the  standards  given  above,  and  that  the  nitrogen- 
content  of  the  abundant  humus  is  amply  within  the  limits  of 
adequacy  suggested  by  the  experience  in  California  and  Ha- 
waii. The  humus-content  of  the  arid  California  soils  is  char- 
acteristically low  as  compared  with  the  Russian  tchernozem 
as  well  as  with  the  Houma  back-land  of  humid  Louisiana; 
but  its  nitrogen-content  is  doubtless  at  least  three  times  that  of 
the  latter,  as  is  that  of  the  humus  of  similar  lands  in  which 
it  has  been  determined. 


THE  ANALYSIS  OF  VIRGIN  SOILS.  365 

INFLUENCE  OF  LIME  UPON   SOIL   FERTILITY. 

Assuming  as  substantially  correct  the  numerical  data  given 
above  in  respect  to  the  three  leading  ingredients  of  plant-food 
— phosphoric  acid,  potash  and  nitrogen, — the  dominant  role 
of  lime  in  soil  fertility,  already  mentioned,  requires  some 
farther  illustration  and  discussion. 

"  A  Lime  Country  is  a  Rich  Country.''-— The  instant  change 
of  vegetation  when  we  pass  from  a  non-calcareous  region  to 
one  having  calcareous  soils,  has  already  been  alluded  to.  (See 
this  chapter,  p.  354).  But  it  is  not  necessary  to  be  a  botanist 
to  see  the  change  in  the  prosperity  of  the  farming  population 
as  one  enters  a  lime  district.  The  single  log-cabin  with,  prob- 
ably, a  wooden  barrel  terminating  the  mud-plastered  chimney, 
is  replaced,  first  by  double  log-houses,  then  by  frame,  and  far- 
ther on  by  brick  buildings,  with  the  other  unmistakable  evi- 
dences of  prosperity.  Thus  this  is  seen  in  passing  from  the 
mountain  region  of  Kentucky  into  the  "  bluegrass  "  country, 
which  is  throughout  underlaid  by  calcareous  formations ;  and 
thus,  likewise,  in  crossing  the  strike  of  the  formations  of  Ala- 
bama, Mississippi  and  Louisiana,  or  any  other  region  where  un- 
derlying calcareous  formations  have  contributed  to  the  for- 
mation of  the  soils,  as  compared  with  some  adjacent  district 
where  this  is  not  the  case.  The  calcareous  loess  areas  border- 
ing on  the  Mississippi  river  and  some  of  its  chief  tributaries, 
are  conspicuous  cases  in  point,  as  are  also  the  prairies  of  Illi- 
nois and  Indiana. 

Effects  of  High  Liinc-contcnt  in  Soils. — The  table  below  il- 
lustrates the  fact  that  in  the  presence  of  high  lime-percentages. 
relatively  low  percentages  of  phosphoric  acid  and  potash  may 
nevertheless  prove  adequate;  while  the  same,  or  even  higher 
amounts,  in  the  absence  of  satisfactory  lime-percentages  prove 
insufficient  for  good  production,1 

1  This  statement  appears  contradictory  of  the  observations  of  Schloesing  fils 
upon  the  solubility  of  phosphoric  acid  in  presence  of  lime  carbonate  (Am.  Sci. 
Agron.,  tome  i,  1X99),  but  the  natural  conditions  seem  to  justify  fully  the  above 
conclusion. 


366 


SOILS. 


If 

^.«00-««0<*^«          «         *         ^0 

.2 

P 

p"            "  " 

H 

3 

O 

«  >> 
53(j 

o> 

00 
ts.   O                                                                                    **'           §             "^   ^ 

o 
>4 

^  x 
EC 

00 

S  o'8«8S-«S55yS'    8-^5  = 

'S. 
c. 

cSS 

"                                      "    *  = 

1 

It 

? 

°1oo"o"Soi-o'o       8       o-     oo 

6- 

1?                                                  "      "  = 

•o  ~ 

~         &. 
o         ^-                            _ 

« 

'S 

Eg 

<CJ 

= 

1  II"                   -  "r 

u 

rt  sj 

^!??S^3«5^?S     ^     -    .?0 

M 

t>.                                                                                     C                 •* 

X 

£ 

Louisiana. 

c  >, 

i! 

4)    O 

5- 

O 
J^     foO    O^U^NOI^M         r>.        ^        «m 

"S. 

£• 

0)     > 

o- 

„      0*5.3   -nKs.y.g        ,«|     .        «0 

8 

II 

.£"                  "°  "           **     ?     -  °° 

s      :::::•:•::•••             ° 
M      .      :....'::"•:. 

"5. 

rt 

x      -^  •  :  :      :  : 

"o 

a     INN  ;^°"  :d'      %         s 

"1 

J      Sfex     "  "°           - 

•E      °^S-3ct"o£§o^'£"             Sb  ^ 

THE  ANALYSIS  OF  VIRGIN  SOILS.  367 

Nos.  1 39  and  171  are  heavy  black  prairie  soils  of  high  productive  capa- 
city, whose  production  had,  at  the  time  of  sampling,  lasted  almost  un- 
diminished  for  over  twenty  years.  Nearly  the  same  is  true  of  the  two 
California  soils,  Nos.  499  and  1113;  which,  however,  are  ferruginous 
loams  of  only  moderate  clay-content.  In  all,  the  percentage  of  phos- 
phoric acid  shown  by  the  analysis  is  at  or  below  the  recognized  limit 
of  deficiency,  while  the  lime-content  of  all  is  as  high  as  is  required  for 
the  welfare  of  any  soil,  however  constituted.  The  potash-percentage 
also  is  low  in  all  except  the  "red  foothill  soil,"  No.  1113. 

Passing  to  the  soils  of  low  lime-content,  we  find  the  two  Mississippi 
soils,  poor  in  both  potash,  lime  and  phosphoric  acid,  so  low  in  produc- 
tion as  to  be  wholly  unprofitable  in  cultivation  without  previous  ferti- 
lization ;  No.  559,  from  California,  produced  two  fair  crops  of  barley 
and  then  no  more.  No.  207,  is  the  soil  of  Eel  river  bottom,  California  ; 
profusely  productive  at  first,  by  virtue  of  its  high  content  of  both  potash 
and  phosphoric  acid;  but  "giving  out"  under  a  few  years'  culture  of 
clover  or  alfalfa  (which  draw  heavily  upon  lime),  and  quickly  restored 
to  productiveness  under  the  influence  of  dressings  of  quicklime.  In 
this  case  the  soil  had  become  acid,  a  condition  which  always  militates 
against  the  success  of  culture  plants,  and  more  especially  against  those 
of  the  leguminous  relationship. 

ll'hat  arc  Adequate  Lime  Percentages? — \Ye  have  in  the 
presence  or  absence  of  the  natural  vegetation  peculiar  to  cal- 
careous soils  ( "  calciphile  ")  an  excellent  index  of  the  pres- 
ence or  absence  of  such  amounts  of  lime  carbonate  as  fulfil  the 
conditions  of  its  beneficial  effects.  Lists  of  such  plants  for  the 
United  States  are  given  farther  on  ;  they  agree  almost  through- 
out with  such  plants  as  arc  everywhere  recognized  by  Ameri- 
can farmers  as  indicating  productive  soils. 

All  soils  bearing  such  vegetation  show  with  red  litmus  paper, 
when  wetted,  a  neutral  reaction  at  first,  which  after  the  lapse  of 
twenty  or  thirty  minutes  turns  to  a  blue  alkaline  one:  such  as 
is  given  under  the  same  conditions  by  the  carbonates  of  lime 
and  magnesia. 

But  the  reverse  is  not  necessarily  true;  for  we  occasionally 
find  soils  containing  considerable  amounts  of  lime  carbonate 
that  yet  fail  to  bear  lime  vegetation.  This  is  the  case  of  ex- 
tremely heavy  clay  soils,  as  exemplified  in  the  table  below 
in  the  case  of  the  last  three  soils;  while  the  first,  Xo.  220.  ex- 


368 


SOILS. 


emplifies  a  case  where,  although  potash  is  exceptionally  high, 
only  scrubby  oak  growth  is  produced  in  presence  of  an  amount 
of  lime  that  in  sandy  lands  would  show  profuse  lime  growth. 

TABLE   ILLUSTRATING  THE   NEED  OF   HIGH    LIME-PERCENTAGES  IN   HEAVY 
CLAY  SOILS. 


Mississippi. 

California. 

Flatwoods, 
Pontotoc 
Co. 

Hog-wal- 
low, Jasper 
Co. 

Ridge 
Prairie, 
Smith  Co. 

Yellow 
ridge,  Ala- 
meda  Co. 

No.  Sample           .  .              

2T.O 

JOj 

4 

CHEMICAL    ANALYSIS   OF   FINE 
EARTH. 

Insoluble  matter  "1 

Soluble  silica  f 

77.85 

76.76 

51.75 

86.00 

Potash  (K»O)  

,7C 

s7 

C-7 

10 

Soda(Na.,O)  

.1  I 

IQ 

1  1 

I  C 

Lime  (CaO)  

.18 

.42 

.48 

48 

Magnesia  MgO  

.ST, 

.67 

I  OI 

AC 

Br.  ox.  of  Manganese  (MnsO.))  .  .  . 
Peroxid  of  Iron  (FeaOs)  

•17 
c.qo 

.56 
A.  12 

.10 

11  7Q 

.04 

4  01 

Alumina  (AlaOs)  

IO.7O 

I  O.o6 

10.81: 

C    C7 

Phosphoric  acid  (PzOs)  

.oc 

.06 

I  c 

•>  •>£ 

.06 

Sulfuric  acid  (SO3)  

O'i 

.06 

O2 

.02 

Carbonic  acid  (CO2)  

\Vater  and  organic  matter  

?.6q 

c  7-j 

I  I   IQ 

A  OC 

Total  

qq86 

QQ  17 

IOO  2Q 

IOO.OQ 

Hygroscopic  Moisture  

Q.-J 

68 

IQ.7 

absorbed  at  °  C 

22  O 

air-dry 

17  O 

All  of  the  soils  in  this  table  are  heavy  clays,  very  difficult  to 
till;  in  all,  the  lime-percentage  falls  below  .$% ',  and  none 
bear  any  lime  vegetation,  the  Mississippi  soils  having  a  stunted 
growth  of  black  jack  and  post  oaks,  such  as  is  universally 
known  to  indicate  soils  too  poor  for  profitable  cultivation.  The 
California  soil  bears  stunted  live  oak  (O.  agrifolia)  ;  but  not 
being  as  heavy  as  its  brethren  from  Mississippi,  though  un- 
thrifty, is  more  readily  improved. 

Comparison  with  the  two  first  sandy  soils  in  the  table  on  p.  352  shows, 
that  with  plant-food  percentages  equal  to,  or  even  much  below  those 
here  shown,  not  only  was  vigorous  lime  growth  present,  but  crop-pro- 
duction was  good  and  even  high. 


THE  ANALYSIS  OF  VIRGIN  SOILS. 


369 


We  are  thus  led  to  the  conclusion  that  the  greater  the  clay 
percentage  in  a  soil,  the  more  lime  carbonate  it  must  contain 
in  order  to  possess  the  advantages  of  a  calcareous  soil;  and 
that  while  in  sandy  lands  lime  growth  may  follow  the  presence 
of  only  .10%  of  lime,  in  heavy  clay  soils  not  less  than  about 
.6%  should  be  present  to  bring  about  the  same  result.  This 
is  apparent  to  the  eye  in  that  the  dark-tinted  humus  characteris- 
tic of  truly  calcareous  lands,  does  not  appear  in  clay  soils  until 
the  lime-percentages  rise  to  nearly  i  %  ;  while  in  sandy  lands  a 
much  smaller  amount  (say  .2%)  will  produce  this  effect. 

European  Standards. — It  is  of  interest  to  consider,  in  connection 
with  preceding  discussions,  the  estimates  given  by  Maercker  of  Halle, 
of  the  practical  value  of  soils  corresponding  to  chemical  composition 
as  ascertained  by  analysis  with  strong  acids,  substantially  in  accordance 
with  the  methods  adopted  by  the  writer. 

PRACTICAL,   RATING  OF  SOILS   BY   PLANT-FOOD   PERCENTAGES  ACCORDING  TO 
PROF.  MAKRCKF.K,    HALLE  STATION,  GERMANY. 


Grade  of  Soil. 

Potash. 

Phosphoric 
Acid. 

Lime. 

Total 
Nitrogen. 

Humus 
Nitrogen. 

Clay  Soil. 

Sandy  Soil. 

poor                

Below  0.05 
0.05  —  o.  15 
0.15  —0.25 
0.25  —  0.40 
Above  0.40 

Below  o  05 
.05  —      10 
.10—      15 
-15—     25 
Above      25 

Below      10 

Below  .05 
.15  -  .20 

.20  .30 

Above  .30 

Relow    05 
.05  —    10 
.10—    15 
.15  —    25 
Above    25 

.102 

(?) 
.166 

.25  —     50 
.50—  I  ex) 
Above  i  oo 

Good             

Kich           

Av'age  for  California.  .  . 
"  Arid  Reg... 
"        "   Humid  Keg. 

0.70 
•73 
•H 

0.08 

.12 
.11 

1.08 
1.36 
.11 

.11 

.12 

It  will  be  observed  that  according  to  Maercker's  valuation,  the  aver- 
age California  soil  is  "  rich  "  in  potash  and  lime,  but  only  "  medium  " 
as  regards  its  contents  of  phosphoric  acid  and  nitrogen.  In  this  respect, 
and  almost  throughout,  Maercker's  ratings  are  in  remarkable  agreement 
with  those  made  by  the  writer  as  far  back  as  1860.'  It  also  appears 
that  Maercker's  figures  for  "  normal"  soils  correspond  to  those  of  the 
American  humid  regions ;  the  "  arid  "  figures  for  potash  and  lime  being 
"  abnormally  "  high. 

1  See  discussions  of  analyses  of  Mississippi  soils  in  the  Report  on  the  Agriculture 
and  Geology  of   Mississippi,   186*1;  same  in   Rep.  On  Cotton   Production,  Tenth 
Census,  1880,  Vol.  5;  also  Appendix  to  the  Report  on  the  Experiment  Stations  of 
the  University  of  California,  1890,  p.  163. 
24 


370 


SOILS. 


Unfortunately  neither  Maercker's  method  of  preparing  the 
soil  extract,  nor  his  ratings  as  given  in  the  table,  are  accepted 
by  all  soil  chemists  even  in  Germany.  As  will  be  seen  by 
reference  to  Wohltmann's  work  on  the  soils  of  Samoa  and 
Kamerun  (chap.  21,  p.  404),  his  methods  and  numerical  esti- 
mates differ  widely  from  those  given  by  Maercker,  and  also 
from  those  adopted  by  the  Prussian  soil  surveys.  Reference  to 
the  analyses  of  the  soils  of  Madagascar  by  Miintz  and  Rous- 
seaux,  given  in  the  same  chapter,  page  406,  shows  still  another 
different  method,  although  as  it  happens  their  numerical  esti- 
mates do  not  differ  very  widely  from  those  of  Wohltmann.  In 
both  cases,  a  special,  more  incisive  extraction  is  made  for  the 
determination  of  potash.  Why  the  same  more  energetic  action 
is  not  used  for  the  other  ingredients  also,  is  not  stated,  and  is 
obscure.  Fortunately,  in  all  cases  the  action  is  at  least  suffi- 
ciently strong  to  secure  the  dissolution  of  all  the  lime  existing 
in  the  form  of  carbonate,  and  of  all,  or  nearly  all,  the  phos- 
phoric acid  not  securely  locked  up  as  ferric  phosphate;  the 
latter  being  inert,  is  of  no  special  interest  (see  Analyses  of 
Hawaiian  Soils,  this  chapter,  page  256). 


CHAPTER  XX. 

SOILS  OF  THE  ARID  AND  HUMID1  REGIONS. 

Composition  of  Good  Medium  Soils. — In  the  preceding1 
tables  examples  have  been  given  of  rather  extreme  types  of 
soils,  both  rich  and  poor  throughout,  and  also  of  such  as  are 
deficient  in  one  or  several  of  the  important  ingredients.  In  the 
table  below  are  given  the  analyses  of  some  of  the  good  aver- 
age farming  lands ;  uplands  of  several  states,  both  of  the  humid 
and  arid  regions.  In  the  former,  the  representative  timber 
trees  of  such  lands  are  the  black,  red,  white  and  (less  charac- 
teristically) the  post,  black-jack,  Spanish,  overcup  and  locally 
some  other  oaks ;  grading  higher  in  proportion  to  the  presence 
of  more  or  less  hickory,  and  lower  as  the  latter  is  replaced  by 
pine.  In  the  states  south  of  Ohio,  the  "  oak  and  hickory  up- 
lands "  are  what  the  farmer  usually  looks  for,  outside  of  the 
valleys  or  bottoms. 

Criteria,  of  Lands  of  the  Ti^o  Regions. — In  the  country  west 
of  the  Rocky  Mountains,  the  timber,  while  locally  very  char- 
acteristic, cannot  be  as  broadly  used  as  a  criterion,  partly  on 
account  of  its  scarcity,  partly  because  the  dominant  factor  in 
the  growth  of  trees  is  moisture,  which  is  measurably  independ- 
ent of  chemical  soil-composition.  The  latter,  moreover,  on  ac- 
count of  climatic  conditions,  already  alluded  to  (chapter  16), 
docs  not  vary  as  materially  in  the  arid  as  the  humid  region,  on 
account  of  the  almost  universal  presence  of  larger  proportions 
of  lime  carbonate;  the  variations  of  which  in  the  humid  region 
govern  largely  the  vegetative  changes.  For  we  there  find  the 
timber  growth  of  the  lowlands  ascending  into  the  uplands  so 

1  Tn  the  discussion  in  this  chapter  the  "  humid  region  "  referred  to  is  always  that 
of  the  temperate  zones,  unless  expressly  otherwise  stated.  The  most  humid  region 
of  all — the  tropics — is  treated  under  a  special  head. 


372 


SOILS. 


i 

rehouse. 

ff 

tC. 

00 

-> 

S 

00                                                                                    O 

,* 

a 

C 

P_ 

JL 

a 

•a 

fa 

od  «                   *  w  «              4      o                  4- 
oo 

LEAVED  I 

umner. 

* 

_f^                                               u 

f?fOP4OONOOOOOOO         OO         GO                                "•*•-• 

(i 

8>"               -  -          N     g 

0 

w 

la 

^   M 

U 

S.3 

u, 

vO 
(> 

•V 

U 

en 

31"              s'S         =    8            :« 

•si 

l§ 

3 
rt 
•a 

0 

•h*,*-.™*  .  --     .2 

u 

6 

00^                                                                                           „            g                                        «M 

.3 
o 

£, 

s 

J^                                                 ° 

O 

«*           ^^       ^    5 

g 

1 

lerokee. 

o 

'^-o««o«-«s?o     «(« 

*" 

U 

l*» 

H 
2 

c 

«     ^00^0^^^          0     ,00 

a 
z 

'3, 
.2< 

c 

« 

oo1                                                         8 

CKORY  A 

1 

ontotoc. 

1 

00 
00 

K 

C-, 

fOiri'           "''«**'         co        5                          •«• 

00 

h 

Q 

o 

a 

c 
c 

itherford. 

^ 

_?_                                                   u 

J 

H 

* 

c^                                                                           O1 

O 

a! 

H      '  :  :  •'  •  :<^  :  :  •'  :  :  : 

a. 
g 

w      :  :            S-    ^  :  :  S                      : 

3 

C/3 

d 
3 
o 
O 

V 

| 

3 

•^       —  >   w  —  /^  C*)  ""               ^^u-^-rt       C^             *^         o»Q 

SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


373 


a  =  g 


_--,!>          •     •         £ 

O    ~   O    r~-  ">  I   O          •     •  •   i 

<>     :  '     2  ' 


SC      'O 

n,    »T          ° 
2  •— *         rt 


" 'S  ^*  ^"r*    r*  •"  ""o  ^-•'C    rt    ^  "^ 


374  SOILS. 

soon  as  the  latter  becomes  decidedly  calcareous;  as  is  abun- 
dantly exemplified  in  the  loess  or  "  bluff  "  formations  border- 
ing the  Mississippi,  Ohio,  and  Missouri  rivers,  where  the  black 
walnut,  tulip  tree,  ash,  honey-locust,  together  with  the  lowland 
oaks,  hickories  and  cane  usually  characterizing  the  stream 
bottoms,  grow  abundantly  and  with  luxuriant  development  on 
the  adjoining  steep  hill  country  as  well  (see  below,  chapters 
24,  2$). 

Soils  of  the  Humid  Region. — Taking  a  view,  first,  of  the 
table  showing  the  soils  of  the  humid  region,  it  appears  that 
the  change  of  vegetation  from  walnut  and  hickory  to  the  short- 
leaved  pine  bears  no  visible  relation  to  the  increase  or  decrease 
of  potash  or  phosphoric  acid,  but  is  plainly  governed  mainly  by 
the  amount  of  lime  present.  Where  the  short-leaved  pine  pre- 
vails the  soil  is  almost  always  either  neutral  or  shows  the 
alkaline  reaction  in  the  course  of  half  an  hour;  but  where  the 
long-leaved  pine  predominates  the  soil  has  almost  always  an 
acid  reaction.  The  latter  is  also  usually  found  in  bottoms  in 
which  the  loblolly  pine  (P.  taeda)  prevails,  and  where,  al- 
though the  soil  may  show  a  fair  proportion  of  lime  in  the 
analysis,  it  does  not  exist  in  the  form  of  carbonate. 

The  examples  here  given  are  from  lands  not  derived  from, 
or  underlaid  by,  limestone  formations.  Where  the  latter  exist 
the  percentage  of  lime  is  usually  materially  increased ;  as  it  is 
also  in  the  lowlands  or  bottoms  when  compared  with  adjacent 
uplands  (see  above,  chapter  10,  p.  162;  chapter  18,  p.  331); 
as  well  as  in  the  delta  lands  of  rivers. 

Soils  of  the  Arid  Region. — Even  a  cursory  comparison  of  the 
soils  of  the  arid  regions  of  the  Pacific  slope  with  those  of  the 
humid,  as  given  in  the  above  tables,  shows  some  striking  points 
of  difference.  The  most  obvious  is  the  uniformly  high  per- 
centage of  lime,  and  usually  also  of  magnesia,  in  the  arid  soils, 
and  that  quite  independently  of  underlying  formations,  calcare- 
ous or  otherwise.  This  occurs  despite  the  fact  that  while  lime- 
stone formations  are  very  prevalent  east  of  the  Rocky  Moun- 
tains, they  are  quite  scarce  west  of  the  same.  The  red  (Lar- 
amie)  sandstones  of  Wyoming,  the  slates  of  the  foothills  of 
the  Sierra  Nevada,  the  clay  shales,  granites  and  eruptives  of 
the  Coast  Ranges  of  California,  Oregon  and  Washington, 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  375 

and  the  varied  black  rocks  of  the  great  lava  sheet  of  the  Pacific 
Northwest,  all  alike  produce  soils  of  high  lime  content  as  com- 
pared with  Eastern  soils  not  derived  from  calcareous  forma- 
tions. This  fact  has  already  been  referred  to,  but  is  more 
fully  illustrated  in  the  table  below. 

Aside  from  the  lime-content,  however,  it  will  be  noted  in  the 
preceding  table  that  the  potash-content  of  the  arid  soils  is  on 
the  average  considerably  higher  than  in  those  of  the  humid 
region.  In  fact  it  is  hard  to  find  west  of  the  Rocky  Mountains 
(except  where  high  elevation  causes  a  humid  climate)  any 
soils  as  poor  in  potash  as  are  many  of  the  commonly  cultivated 
lands  of  the  Eastern  United  States. 

Other  ingredients  do  not  show  such  marked  differences  from 
the  purely  chemical  standpoint :  yet,  as  will  be  shown  below, 
the  forms  in  which  silica  and  alumina  occur  are  also  not  incon- 
siderably modified. 

GEXERAL  COMPARISON  OF  SOILS  FROM  THE  ARID  AND 
HUMID  REGIONS  OF  THE  UNITED  STATES.1 — In  order  to 
verify  the  conclusions  just  mentioned  upon  the  broadest  basis 
possible,  the  following  table  has  been  compiled  from  all  avail- 
able sources;  partly  published,  partly  in  manuscript  only,  hav- 
ing remained  in  the  writer's  hands  since  the  cessation  of  the 
Northern  Transcontinental  Survey,  prosecuted  from  1880  to 
1883,  under  the  auspices  of  the  Northern  Pacific  Railroad,  in 
Washington  and  Montana.  The  published  data  are  derived 
partly  from  the  records  of  State  surveys,  partly  from  the  soil 
work  connected  with  the  Tenth  Census;  partly  also  from  those 
of  Experiment  Stations.  In  most  cases  it  has  of  course  been 
necessary  to  restrict  the  comparison  to  such  analyses  as  have 
been  made  by  substantially  identical  methods,  for  reasons  al- 
ready given  ;  but  in  the  cases  of  some  states  from  which  numer- 
ous analyses  made  by  the  Kedxie  method,  adopted  by  the  As- 
sociation of  Official  Chemists,  were  available,  the  average  has 
been  given  but  the  name  of  the  state  starred,  to  indicate  that 
the  percentages,  excepting  phosphoric  acid,  are  lower  than  they 
would  be  if  made  by  the  method  adopted  by  the  writer,  par- 
ticularly as  regards  potash.  The  adoption  of  the  one-milli- 
meter mesh  for  the  fine-earth  sieve  instead  of  the  half-milli- 

1  Abstracted  and  revised  from  Bulletin  No.  3.  U.  S.  Weather  Bureau,  1893. 


376  SOILS, 

meter  size  also  creates  an  unfortunate  and  ineliminable  dis- 
crepancy. 

In  order  to  exhibit  clearly  the  influence  of  climate  as  distinct 
from  other  local  conditions,  it  was  also  necessary  to  eliminate, 
in  both  the  arid  and  humid  regions,  the  soils  directly  derived 
from,  or  connected  with  calcareous  formations;  such  as  the 
prairies  of  the  Southwestern  States,  the  Bluegrass  region  of 
Kentucky,  etc.  This  rule  having  been  applied  impartially  to 
the  soils  of  both  climatic  regions,  it  can  hardly  be  questioned 
that  the  conclusions  flowing  from  a  discussion  of  the  results  of 
the  comparison  are  entitled  to  as  much  weight  as  are  those  of 
any  comparison  based  on  large  numbers  of  observations  made, 
not  with  reference  to  the  special  point  under  consideration,  but 
with  a  practical  object  of  which  the  governing  conditions  were 
more  or  less  uncertain,  and  required  to  be  ascertained  by  a  pro- 
cess of  elimination. 

The  table  gives,  first,  the  averages  for  each  ingredient  for  each  of  the 
states  represented,  the  number  of  analyses  from  which  the  averages  are 
derived  being  given  in  each  case.  These  averages  are  given  separately 
for  the  states  of  the  humid  and  the  arid  regions  respectively ;  and  at 
the  base  of  each  group  the  grand  average  is  shown  in  two  forms.  The 
first  gives  the  figures  as  derived  from  the  aggregate  number  of  soil 
analyses  in  each  great  group,  being  696  for  the  humid,  178  for  the 
transition  region  and  573  for  the  arid,  divided  into  the  totals  resulting 
from  the  summation  of  each  ingredient  for  the  whole  696,  178  and  573, 
respectively. 

The  second  form  is  that  in  which  the  soils  of  each  state  are  considered 
as  representative  of  the  general  character  of  such  state,  as  the  result  of 
intentional  selection ;  such  as  actually  occurred  in  the  cases  of  those 
included  in  the  census  work  of  1880.  The  figures  given  here  are 
therefore  the  result  of  a  summation  of  the  state  averages  as  such,  and 
of  their  division  by  the  number  of  states  represented. 

It  will  be  noted  that  while  these  two  modes  of  presentation  do  change 
the  figures  a  little,  yet  in  either  form  the  same  general  result  is  out- 
lined with  striking  accuracy.  It  is  also  notable  that  notwithstanding 
the  less  complete  extraction  of  soil-ingredients  in  the  starred  states, 
the  general  ratios  between  arid  and  humid  soils  remain  substantially 
the  same.  For  Western  Oregon,  local  calcareous  formations  compel 
omission  of  three  lime  figures  from  the  averages. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


377 


'[log  UT 


snuinpj  ui 


PUB 


i  o  ••f      o    o   o 


•ppy 


"Ooqooco      >-    o    o          ooo          o;«o;o-o      ~  o    o    o 


•ppy 

DIJ<U(dsOl|(J 


UOJ[  JO 


OOOOO--ONN-         O      -      i-> 


o  o  o  o  - 


1O          "-.O     -O 


oc  00    t^   00 


•f.  -5 

•o  ^ 

S  —       u  ^  ,c    :    o 

3!  s  K11'  §  i 

^s2     ^  w*.  '&    ^ 


< 


378  SOILS. 

New  Mexico. — Few  analyses  of  New  Mexico  soils  have  been 
made,  but  the  average  results  of  six  partial  determinations 
made  by  Goss,  and  one  full  analysis  made  by  Hare  according 
to  the  method  of  the  writer,  and  given  below,  show  substantial 
accord  with  the  averages  of  the  above  table.  The  averages  of 
Goss'  determinations  are :  Potash  .780,  Phosphoric  acid 
.221,  Nitrogen  .108  per  cent. 

CHEMICAL  ANALYSIS  OF   RIO   GRANDE  SILT  (by   Prof.   R.   F.   Hare.) 

Deposited  on  on  land  by  irrigation. 

Insoluble  matter 63.70 

Potash  ( KaO) i  .06 

Soda  NaaO) 22 

Lime  (CaO) 4.97 

Magnesia  ( MgO) 2.43 

Br.  ox.  of  Manganese  (MnsO,i) .14 

Peroxid  of  Iron  (Fe^Os) 5.80 

Alumina  (AUO3) 6.86 

Phosphoric  acid  (P3O6) .16 

Sulfuric  acid  (SOn) . .13 

Carbonic  acid  (CO2) 7.45 

Water  and  organic  matter 9.98 

Humus 1.17 

"         Nitrogen 1 1 .1 1 

"  "         per  cent,  in  soil .13 

Hygroscopic  Moisture 2.63 

absorbed  at ...°C     .... 


DISCUSSION   OF   THE   TABLE. 

Lime. — Considering  in  this  table,  first,  lime,  a  glance  at  the 
columns  for  the  two  regions  shows  a  surprising  and  evidently 
intrinsic  and  material  difference,  approximating  in  the  average 
by  totals  to  the  proportion  of  i  to  1 1 ;  in  the  average  by  states, 
i  to  14  l/2.  This  difference  is  so  great  that  no  accidental  errors 
in  the  selection  or  analysis  of  the  soils  can  to  any  material  de- 
gree weaken  the  overwhelming  proof  of  the  correctness  of  the 
inference  drawn  upon  theoretical  grounds,  viz.,  that  the  soils  of 
the  arid  regions  must  be  richer  in  lime  than  those  of  the  humid 
countries.  For  the  differences  in  derivation  would,  in  view  of 
the  wide  prevalence  of  limestone  formations  in  the  humid 
regions  concerned,  produce  exactly  the  reverse  condition  of 
things  from  that  which  is  actually  found  to  exist ;  and  if  fur- 
ther proof  were  needed  it  can  readily  be  found  in  the  detailed 
discussion  of  the  analyses  of  the  soils  of  the  arid  areas  forming 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  379 

the  contrast.  This  shows  that  for  instance,  in  Washington 
highly  calcareous  soils  are  directly  derived  from  the  black 
basaltic  rocks;  while  similarly,  calcareous  lands  are  found  in 
California  to  be  the  outcome  of  the  decomposition  of  granites, 
diorites,  lavas,  clay-shales  and  sandstones. 

It  is  not  easy  to  overrate  the  importance  of  this  feature  of 
the  soils  of  the  arid  region,  as  it  is  intimately  connected  with 
other  theoretically  and  practically  important  facts,  in  part  al- 
ready mentioned. 

Summary  of  Effects  of  Lime  Carbonate  in  Soils. — It  is  best 
to  summarize,  briefly,  at  this  point,  the  advantages  (and  possi- 
ble disadvantages),  resulting  from  the  presence  of  a  proper 
amount  of  lime  carbonate  in  soils,  so  far  as  these  are  at  present 
understood. 

Physically,  even  a  small  amount  of  lime  carbonate,  by  its 
solubility  in  the  carbonated  soil-water,  will  act  most  beneficially 
in  causing  the  flocculation  of  clay  and  in  the  subsequent  con- 
servation of  the  flocculent  or  tilth  condition,  by  acting  as  a 
light  cement  holding  the  soil-crumbs  together  when  the  capil- 
lary water  has  evaporated ;  thus  favoring  the  penetration  of 
both  water  and  air,  and  of  the  roots  themselves.  It  should  be 
added  that  according  to  the  experience  of  the  writer,  amounts 
of  lime  carbonate  in  excess  of  2%  do  not  add  to  the  favorable 
effects,  except  as  would  so  much  sand. 

As  to  chemical  effects,  among  the  most  important  are : — 

1.  The  maintenance  of  the  neutrality  of  the  soil,  by  the 
neutralization  of  acids  formed  by  the  decay  of  organic  matter, 
or  otherwise. 

2.  The  maintenance,  in  connection  with  the  proper  degrees 
of  moisture  and  warmth,  of  the  conditions  of  abundant  bac- 
terial life  (see  above,  chapter  o,.  p.  146)  ;  more  especially  those 
of  nitrification,  thus  supplying  the  readily  assimilable  form  of 
nitrogen.     Also  in  favoring  the  development  and  activity  of 
the  root  bacteria  of  legumes,  and  of  the  other  nitrogen-gather- 
ing bacteria,  such  as  Azotobacter  (ibid.  p.  156). 

3.  The   rendering   available,    directly  or   indirectly,   of   re- 
latively small   percentages  of  plant-food,   notably  phosphoric 
acid  and  potash  ;  as  shown  in  the  preceding  pages. 

4.  The  prompt  conversion  of  vegetable  matter  into  black, 


380  SOILS. 

neutral  humus,  and  (as  shown  in  the  case  of  the  soils  of  the 
arid  region)  the  concentration  of  the  nitrogen  in  the  same; 
while  accelerating  the  oxidation  of  the  carbon  and  hydrogen, 
as  shown  by  S.  W.  Johnson  and  others. 

6.  It  counteracts  the  deleterious  influence  of  an  excess  of 
magnesia  in  the  soil,  as  first  shown  by  Loew,1  and  verified  by 
his  pupils  in  Japan. 

7.  In  alkali  soils,  according  to  Cameron  and  May,  it  coun- 
teracts  the    injurious    action    of   the    soluble    salts   upon    the 
growth  of  plants,  not  only  in  the  form  of  carbonate,  but  also  in 
those  of  sulfate  and  chlorid.2 

8.  As  a  matter  of  experience,  both  in  the  case  of  grapes  and 
orchard  as  well  as  wild  fruits,  an  adequate  but  not  excessive 
supply  of  lime  in  the  soil  will  produce  sweeter  fruit  than  when 
lime  is  in  small  supply. 

9.  An  excess  of  carbonate  of  lime  in  soils   (from  eight  to 
twenty  per  cent  and  more),  constituting  "  marliness,"  tends  to 
seriously  disturb  the  nutrition  and  general  functions  of  many 
plants  (calcifuge),  and  to  produce  a  suppression  or  diminution 
of  the  formation  of  chlorophyll  and  starch ;  as  in  the  case  of 
grape  vines,  citrus  fruits  and  others,  which  nevertheless  flour- 
ish best  in  lands  moderately  calcareous. 

Among  the  points  thus  enumerated  the  third  and  fourth  re- 
quire some  comment.  Without  pretending  to  define  exactly 
how  lime  acts  in  rendering  other  ingredients  more  available  to 
plant  assimilation,  attention  may  be  called  to  the  fact  that  lime 
carbonate  may  be  considered  as  acting  similarly  to,  albeit  more 
mildly  than,  caustic  lime,  in  the  displacement  of  other  bases 
from  their  compounds.  It  doubtless  acts  thus  in  liberating 
potash  from  its  zeolitic  compounds.  As  to  phosphoric  acid, 
the  connection  of  the  effect  of  lime  carbonate  with  the  remark- 
able availability  of  that  substance  when  present  in  the  form  of 
tetra-basic  salt,  in  the  case  of  phosphate  slag,  is  at  least  possible. 

As  to  the  action  of  lime  carbonate  in  forming  humus,3  no  one  who 
has  observed  the  characteristic  dark  black  tint  of  our  calcareous 

1  Bull.  No.  I,  Div.  Veget.   Physiol.  and  Plant  Pathol.  U.  S.  Dept.  Agr. ;  et  al. 

2  Loeb  (Publications  of  the  Spreckel's   Physiological  Laboratory  of  the  Univer- 
sity  of  California,  has  shown  a  similar  protective  influence  of  the  lime  salts  in 
sea-water,  against  the  other  salts,  in  the  case  of  the  lower  marine  organisms. 

3  "  Black  Soils  ;  "  Agric.  Science,  January,  1892. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  381 

"  prairie  soils  "  can  question  the  fact ;  which  moreover  is  perfectly  ex- 
plicable upon  the  analogy  already  alluded  to,  with  caustic  lime,  which, 
together  with  caustic  alkalies  (potash  and  soda),  is  known  to  act  power- 
fully in  the  conversion  of  vegetable  matter  into  humus.  That  instead 
of  liberating  the  nitrogen  in  the  form  of  ammonia,  as  do  the  caustic 
hydrates,  the  milder  carbonate  should  only  cause  the  formation  of  humic 
amides,  is  quite  intelligible.  That  such  is  really  the  case,  has  been 
conclusively  proved  by  the  investigations  of  the  writer  made  conjointly 
with  M.  E.  Jaffa  (Rep.  Sta.  Cal.  Agr.  Expt.  1892-4) ;  the  general  result 
being  that  while  in  the  humid  region  the  average  nitrogen-content  of 
soil-humus  is  less  than  5  r/c,  in  the  upland  soils  of  the  arid  region 
(where  all  soils  are  calcareous)  that  percentage  rises  as  high  as  22.0%, 
with  a  general  average  of  between  15  and  16%.  That  such  highly 
nitrogenous  material  can  be  more  readily  attacked  by  the  nitrifying 
bacteria  than  when  a  large  excess  of  other  oxidable  matter  is  present, 
is  at  least  a  legitimate  presumption,  especially  in  view  of  the  very  active 
nitrification  known  to  take  place  in  the  arid  regions  everywhere.  So 
long  as  a  large  excess  of  carbohydrates  is  present,  the  oxidation  of  these 
will  naturally  take  precedence  over  that  of  the  relatively  inert  nitrogen. 
The  accumulation  of  the  latter  in  the  humus-substance  of  the  arid 
region,  where  oxidation  of  the  organic  matter  of  the  soil  is  very  active, 
points  strongly  to  this  view  of  the  case. 

Magnesia. — While  the  differences  in  respect  to  the  propor- 
tions of  lime  are  the  most  prominent  and  decided,  yet  the  re- 
lated substance,  magnesia,  shows  also  a  very  marked  and  con- 
stant difference  as  between  the  soils  of  the  humid  and  arid 
regions.  It  will  be  observed  that  the  general  average  for  mag- 
nesia in  the  soils  of  the  Atlantic  Slope  is  about  double  that  of 
lime;  Florida  and  Rhode  Island  being  the  only  states  in  which 
the  average  is  lower  for  magnesia  than  for  lime.  In  the 
arid  region,  on  the  contrary,  magnesia  on  the  general  average 
is  nearly  the  same  as  lime;  in  the  average  by  states,  some- 
what less;  thus  bringing  the  ratio  for  the  two  regions  for  mag- 
nesia up  to  one  to  six  or  seven.  This  also  is  so  decisive  a 
showing  that  no  accident  could  bring  it  about.  We  must  con- 
clude that  climatic  influences  have  dealt  with  magnesia  simi- 
larly as  witli  lime;  which  from  the  standpoint  of  the  chemist  is 
just  what  might  he  expected,  since  magnesia  carbonate  behaves 
very  much  like  that  of  lime  toward  carbonated  waters. 


382  SOILS. 

That  magnesia  is  a  very  important  plant-food  ingredient  is 
apparent  from  its  invariable  and  rather  abundant  presence  in 
the  seeds  of  plants,  where  it  takes  precedence  of  lime.  Its  func- 
tions in  plant  nutrition  have  been  specially  investigated  by  O. 
Loew,1  particularly  with  respect  to  its  relations  to  lime.  As 
already  stated  in  connection  with  the  soil-forming  properties 
of  magnesian  minerals  (see  chapter  2),  soils  containing  large 
proportions  of  magnesia  generally  are  found  to  be  unthrifty, 
the  lands  so  constituted  being  frequently  designated  as  "  bar- 
rens." Loew  finds  that  certain  proportions  of  lime  to  magnesia 
must  be  preserved  if  production  is  to  be  satisfactory,  the  pro- 
portion varying  with  different  plants,  some  of  which  (e.  g. 
oats)  will  do  well  when  the  proportion  of  lime  to  magnesia  is 
as  i  :i,  while  others  require,  that  that  ratio  should  be  as  2  or  3 
is  to  i,  to  secure  the  best  results.  In  general  it  is  best  that 
lime  should  exceed  magnesia  in  amount. 

Loew  explains  the  injurious  action  of  magnesium  salts  thus  :  The 
calcium  nucleo-proteids  of  the  organic  structures  are  transformed  in 
presence  of  soluble  salts  of  magnesium  into  magnesium  compounds, 
while  the  calcium  of  the  former  enters  into  combination  with  the  acid 
of  the  magnesium  salt.  By  this  transformation  the  capacity  for  im- 
bibition will  change,  which  must  result  in  a  fatal  disturbance  of  functions. 
The  presence  of  soluble  lime-salts  will  prevent  that  interchange.  Thus 
certain  algae  perished  in  a  solution  containing  i  per  1000  of  magnesium 
nitrate,  but  remained  alive  when  .3  per  1000  of  calcium  nitrate  was 
added. 

Magnesia  seems  to  be  specially  concerned  in  the  transfer  of 
phosphoric  acid  through  the  plant  tissues,  in  the  form  of 
dimagnesic-hydric  phosphate,  which  is  rather  soluble  in  the 
acid  juices  of  plants.  It  is  probable  that,  apart  from  the  re- 
lations just  referred  to,  such  excess  of  lime  as  is  known  to  pro- 
duce chlorosis  in  plants  interferes  with  the  transfer  of  the  mag- 
nesic  phosphate.  Some  plants,  as  already  stated,  dispose  of  an 
excess  of  lime  by  depositing  it  in  the  form  of  oxalate,  while 
others  (such  as  the  stone  crops)  excrete  it  on  the  surface  of 

1  Bull.  No.  18,  Div.  Vegetable  Physiology  and  Plant  Pathology;  Bull.  No.  I 
Bureau  of  Plant  Industry,  U.  S.  Dept.  of  Agr. ;  Bull.  College  of  Agriculture,  Tokyof 
Vol.  4,  No.  5. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  383 

leaves  and  stems  in  the  form  of  carbonate.     But  others  seem 
to  possess  this  power  to  a  limited  extent  only. 

In  the  case  of  soils  containing  much  magnesia  the  proper 
proportion  between  it  and  lime  may  easily  be  disturbed  by  the 
greater  ease  with  which  lime  carbonate  is  carried  away  by  car- 
bonated water  into  the  subsoil,  thus  leaving  the  magnesia  in 
undesirable  excess  in  the  surface  soil.  Hence  the  great  ad- 
vantage of  having  in  a  soil,  from  the  outset,  an  ample  propor- 
tion of  lime.  From  this  point  of  view  alone,  then,  the  analyti- 
cal determination  of  lime  and  magnesia  in  soils  is  of  high 
practical  value. 

Aso,  Furuta  and  Katayama  (Bull.  Coll.  Agr.  Tokyo,  Vol.  4  No.  5  ; 
Ibid.  Vol.  6),  have  by  direct  experiment  determined  the  most  advan- 
tageous ratio  of  lime  to  magnesia  in  several  crop  plants.  They  find 
for  rice  and  oats  i  :  i,  for  cabbage  2:1,  for  buckwheat  3:1;  there  being 
apparently  a  connection  between  the  extent  of  leaf-surface  and  lime 
requirement,  since  leaves  contain  predominantly  lime,  while  in  the  fruit, 
magnesia  predominates. 

Manganese. — A  decided  difference  in  the  manganese  content 
of  the  arid  as  against  the  humid  soils  appears  in  the  table,  the 
ratio  being  about  11  :  13  in  favor  of  the  humid  soils.  Man- 
ganese has  not  been  regarded  as  being  of  special  importance  to 
plant  growth  in  general,  although,  as  already  stated,  some 
plants  contain  a  relatively  large  proportion  of  manganese  in 
their  ashes ;  thus,  e.  g.,  the  leaves  of  the  long-leaved  pine  of  the 
cotton  states.1  But  no  definite  data  showing  the  importance  of 
this  element  to  crops  were  available  until  Loew  and  his  co- 
workers  at  Tokyo  2  established  its  stimulating  action  in  a  num- 
ber of  cases,  in  which  crop  production  was  materially  increased 
by  the  use  of  protoxid  salts  of  manganese.  Aso  a  applied  man- 
ganous  chlorid  to  an  experimental  plot  of  thirty  square  meters, 
at  the  rate  of  twenty-five  kilos  of  Mn.,O4  per  acre,  and  thus 
obtained  a  yield  of  rice  one-third  greater  than  on  the  control 
plot,  at  a  cost  of  about  $2.00,  while  the  value  of  the  increase 
of  the  product  was  nearly  $68.00.  More  experimental  evi- 
dence on  this  subject  is  required  to  establish  the  general  value 

1  Rep.  Agr.  and  Geology  of  Mississippi,  1860,  p.  360. 

»  Bull.  Agr.  Coll.  Tokyo,  Vol.  V.,  Xos.  2  and  4.  »  Ibid.  Vol.  6. 


384  SOILS. 

of  the  large-scale  use  of  the  salts  of  manganese;  which  are 
obtained  in  large  quantities  as  a  comparatively  valueless  by- 
product of  the  bleaching  industries. 

The  "  Insoluble  Residue." 

Remembering,  in  discussing  the  facts  shown  by  the  table, 
that  the  fundamental  difference  between  the  regime  of  the 
humid  and  arid  regions  is  the  presence  in  the  latter  of  an  al- 
most continuous  leaching  process,  in  which  the  carbonated 
water  of  the  soil  is  the  solvent;  remembering,  also,  that  the 
least  soluble  portion  of  rocks  and  soils  is  quartz  or  silica  ( sand, 
as  usually  understood),  it  would  be  predicable  that  this  ingredi- 
ent should  in  the  humid  region  be  found  to  be  more  abundant 
in  soils  than  in  the  arid.  This  portion  is  represented  by  the 
"  insoluble  residue  "  of  the  table. 

Inspection  shows  that  both  in  the  averages  of  the  single 
states,  and  in  both  of  the  general  averages,  this  difference  be- 
tween the  soils  of  the  humid  and  the  arid  regions  of  the  United 
States  is  strongly  pronounced ;  the  ratio  being  substantially  as 
69%  in  the  arid  region  to  84%  in  the  humid. 

We  must  then  conclude  that  the  leaching  process  must  have 
influenced  materially  other  soil  ingredients  than  lime,  which 
have  remained  behind  in  such  amounts  as  to  depress  the  per- 
centage of  insoluble  residue  in  the  soils.  It  remains  to  be 
shown  what  are  the  substances  so  retained. 

Insoluble  and  Soluble  Silica  and  Alumina. 

The  ingredient  most  nearly  correlated  with  the  insoluble 
residue  is  the  free  silica  which  remains  behind  with  it  when  the 
acid  with  which  the  soil  has  been  treated  is  evaporated  to  dry- 
ness.  The  silica  is  separated  from  the  practically  insoluble, 
undecomposed  minerals  by  boiling  with  a  strong  solution  of 
sodic  carbonate.  The  amount  of  this  "  soluble  silica  "  is  obvi- 
ously the  measure  of  the  extent  to  which  the  soil-silicates  have 
been  decomposed  in  the  treatment  with  acid. 

The  most  prominent  of  these  is  usually  supposed  to  be  clay — 
the  hydrous  silicate  of  alumina  that  in  its  purest  condition 
forms  kaolinite  or  porcelain  earth.  Any  alumina  found  in  the 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  385 

usual  course  of  soil  analysis  is  generally  referred  to  this  min- 
eral, which  contains  silica  and  alumina  nearly  in  the  proportion 
of  46%  to  40%. 

In  very  many  cases,  however,  the  reference  of  these  two  in- 
gredients to  clay  is  manifestly  unjustified.  This  is  clearly  so 
when  (as  not  unfrequently  happens)  the  amount  of  alumina 
found  exceeds  that  which  would  form  clay  with  the  ascertained 
percentage  of  soluhle  silica ;  it  is  almost  as  certainly  so  when, 
in  addition  to  the  alumina,  other  bases  (notably  potash,  lime 
and  magnesia),  are  found  in  proportions  which  preclude  their 
being  in  combination  with  any  other  acidic  compounds  pres- 
ent. The  only  possible  inference  in  such  cases  is  that  these 
bases,  together  with  at  least  a  portion  of  the  alumina,  are  pres- 
ent in  the  form  of  hydrated,  and  therefore  easily  decomposable 
silicates  or  zeolites. 

The  subjoined  analysis  by  R.  H.  Loughridge,  of  a  clay  obtained  in 
the  usual  process  of  mechanical  soil  analysis  (by  precipitating  with  com- 
mon salt  the  turbid  water  remaining  after  24  hours  subsidence  in  a 
column  of  200  millimeters)  from  a  very  generalized  soil  of  northern 
Mississippi,  shows  one  of  the  many  cases  in  which  the  numerical  ratios 
of  the  several  ingredients  are  incompatible  with  the  assumption  that 
silica  and  alumina  are  present  in  combination  as  clay  (kaolinite)  only  : 

ANALYSIS   OF   COLLOIDAL   CLAY. 

Insoluble  matter 1 5.96 

Soluble  silica 3.v'O 

Potash  K3O) 1.47 

Soda  (Na^O) 1.70 

Lime  (  Ca( )) 09 

Magnesia  (MgO) 1.33 

Hr.  ox.  of   Manganese  (MnaO«) .}o 

I'eroxid  of  iron  ( FejOa 18.76 

Alumina  (AM  )3 > 18.19 

Phosphoric  acid  (I'sOi) .iS 

Sulfuric  acid  (S()3) .06 

Carbonic  acid  (COj) .00 

Water  and  organic  matter Q.oo 


Total i  oo.  1 4 

If  in  this  case  we  assign  all  alumina  to  silica,  as  required  for  the 
composition  of  kaolinite  or  pure  clay,  there  yet  remains  a  trifle  over 
twelve  (i  2.1  7)  per  cent  of  silica  to  be  allotted  to  the  other  bases  present. 
Deducting  from  this  the  ascertained  amount  of  silica  soluble  in  sodic 
carbonate,  pre-existing  in  the  raw  material  (.38  per  cent),  we  come  to 
11.79  per  cent,  as  the  amount  of  silica  which  must  have  been  in  com- 
25 


386  SOILS. 

binations  other  than  kaolinite,  viz.,  hydrous  silicates,  or  soil  zeolites, 
formed  either  with  the  bases  other  than  alumina  shown  in  the  analysis 
or,  more  probably,  containing  some  of  the  alumina  itself  in  essential 
combination. 

We  are  thus  enabled  to  obtain  from  the  determination  of  the  soluble 
silica  an  estimate  of  the  extent  to  which  these  soil  zeolites,  that  form 
so  important  a  portion  of  the  soil  in  being  the  repositories  of  the  reserve 
of  more  or  less  available  mineral  plant-food,  are  present  in  the  soils  of 
the  several  regions.  A  glance  at  the  table  shows  that  the  general 
average  of  soluble  silica  is  very  much  greater  in  the  soils  of  the  arid 
regions  than  in  those  of  the  humid,  approximating  one  to  two  in  favor 
of  the  arid  division.' 

Differences  in  the  Sands  of  the  Arid  and  Humid  Regions. — 
In  chapter  5  mention  has  been  made  of  the  fact  that  while 
in  the  humid  regions,  "  sand  "  as  a  rule  means  quartz  grains, 
mostly  with  a  clean  surface  and  very  frequently  rounded  and 
polished,  in  the  arid  regions  even  the  coarse  sand  grains  consist 
of,  or  are  covered  with,  a  great  variety  of  minerals  in  a  parti- 
ally decomposed  condition.  This  is  owing  to  the  absence  of 
the  abundant  rainfall  which  in  humid  climates  continually 
washes  down  the  finely  divided,  half-decomposed  mineral  mat- 
ter into  the  subsoil ;  while  in  arid  climates  the  light  rains  can- 
not produce  any  such  washing  effect  and  hence  the  sand  grains 
remain  incrusted  with  the  products  of  either  their  own  decom- 
position, or  of  that  of  neighboring  particles;  it  being  therefore 
not  concentrated  in  the  finer  portion  only,  viz.,  the  clay  and 
finest  silts.  This  fundamental  difference,  which  is  illustrated 
in  the  analytical  table  below,  at  once  explains  why  in  the  arid 
regions  generally,  sandy  soils  are  found  so  highly  productive 
that,  owing  to  their  easy  cultivation  they  are  preferred  to  the 
clayey  lands,  in  which  tillage  and  irrigation  are  more  difficult. 

1  Looking  at  the  details  of  the  several  states,  we  find  that  on  the  arid  side 
Washington  has  a  relatively  low  figure  for  soluble  silica,  which  in  the  average,  how 
ever,  is  overborne  by  the  high  figures  for  California  and  Montana.  The  explana- 
tion of  this  fact  probably  lies  in  the  derivation  of  the  majority  of  the  Washington 
soils  examined,  from  lake  deposits  brought  down  gradually  from  the  humid  region 
at  the  heads  of  the  Columbia  drainage,  where 'sandy  beds  are  very  prevalent, 
while  the  country  rock — the  basaltic  eruptives — are  very  basic,  and  moreover  slow 
to  disintegrate.  In  California  and  Montana  the  rocks  are  infinitely  varied,  and  the 
general  outcome  of  their  weathering  is  plainly  a  predominance  of  complex  hydrous 
silicates  in  the  soils,  as  compared  with  humid  regions. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


387 


It  is  a  well-known  fact  that  on  the  "  sands  of  the  desert  "  when 
either  irrigated,  or  wetted  by  rain,  vegetation  at  once  springs 
up  with  remarkable  luxuriance,  even  on  sand  drifts;  and  this 
productiveness  appears  to  be  quite  as  lasting  as  that  of 
"  strong  "  clay  soils  of  the  humid  regions. 

This  difference  is  curiously  illustrated  on  the  southern  edge  of  the 
"black  adobe"  or  prairie  soil  area  which  surrounds  Stockton,  Cal. 
Here  we  find  on  the  opposite  sides  of  a  small  stream  (French  Camp 
slough)  the  two  extremes,  of  heavy  clay  and  the  sandy  soils  which  for 
many  years  made  Stanislaus  county  the  "  banner  "  county  for  wheat. 
The  grain  product  of  both  banks  ranked  alike  in  quantity  and  quality 
in  average  years ;  but  in  extreme  seasons  sometimes  one,  sometimes  the 
other  failed,  according  to  the  weather  conditions  which  favored  one  or 
the  other  soil.  No  one  would  think  of  sowing  wheat  on  so  sandy  a 
soil  in  the  humid  States. 

TAHLE    ILLUSTRATING    DIFFERENCE   IN    SANDS    OF   THE   HUMID  AND  ARID  REGIONS. 


Clay. 

Per  cent  in 
Soil. 

Potash. 

w 

2 

Magnesia  . 

c 

J:t3 

CX'G 

I** 

PH 

I  .8 
I3 

Alumina. 

Summation. 

21   64 

•32 

California  1281  C'hino2  

7  60 

.16 

.14 

08 

2  83 

3  56 

5-34 

if-, 

07 

2  87 

i  -*6 

18  53 

06 

i  -f. 

5'22 

7.84 

.04 

5.18 

13  67 

' 

g 

9  9° 

.08 

' 

' 

1.50 

2.25 

7  68 

<>6 

<K>6 

o  82 

.02 

1.70 

6  An 

S  i  i 

.07 

.01 

,CM>3 

<i6 

1.79 

Fine  sand  .072  —.12  mm.  diam  

1  1  87 

.013 

•77 

•  *° 

i-43 

4      3 

.0 

.005 

.40 

•\(->  1  1 

i 

2-43 

1.59 

It  thus  appears  that  while  in  the  Mississippi  soil,  solubility  of 
plant-food  practically  ceased  at  grain-diameter  of  .030  mm.  in 


1  Analyses  by  K.  II.  Loughridge. 
E.  II.  Lea. 


Analyses  by  L.  M.  Tolman.      8  Analyses  by 


388  SOILS. 

the  arid  California  soils,  as  large  an  amount  was  found  in 
the  sand-grain  sizes  between  .12  and  .50  millimeters  as  in  the 
fine  silt  .016  to  .025  mm.  in  Mississippi. 

Hydrous  Silicates  are  More  Abundant  in  Arid  than  Humid 
Soils. — This  predominance  of  hydrous  silicates  in  the  soils  of 
the  arid  regions  should  not  be  a  matter  of  surprise  when  we 
consider  the  agencies  which  are  brought  to  bear  upon  these  soils 
with  so  much  greater  intensity  than  can  be  the  case  where  the 
solutions  resulting  from  the  weathering  process  are  continu- 
ally removed  as  fast  as  formed,  by  the  continuous  leaching 
effect  of  atmospheric  waters.  In  the  soils  of  regions  where 
summer  rains  are  insignificant  or  wanting,  these  solutions  not 
only  remain,  but  are  concentrated  by  evaporation  to  a  point 
that,  in  the  nature  of  the  case,  can  never  be  reached  in  humid 
climates.  Prominent  among  these  soluble  ingredients  are  the 
silicates  and  carbonates  of  the  two  alkalies,  potash  and  soda. 
The  former,  when  filtered  through  a  soil  containing  the  carbon- 
ates of  lime  and  magnesia,  will  soon  be  transformed  into  com- 
plex silicates,  in  which  potash  takes  precedence  of  soda,  and 
which,  existing  in  a  very  finely  divided  (at  the  outset  in  a 
gelatinous)  condition,  serve  as  an  ever-ready  reservoir  to 
catch  and  store  the  lingering  alkalies  as  they  are  set  free  from 
the  rocks,  whether  in  the  form  of  soluble  silicates  or  carbonates. 
The  latter  have  another  important  effect :  in  the  concentrated 
form  at  least,  they,  themselves,  are  effective  in  decomposing 
silicate  minerals  refractory  to  milder  agencies,  such  as  calcic 
carbonate  solution;  and  thus  the  more  decomposed  state  in 
wThich  we  find  the  soil  minerals  of  the  arid  regions  is  intelligi- 
ble on  that  ground  alone. 

It  must  not  be  forgotten  that  lime  carbonate,  though  less  effective 
than  the  corresponding  alkali  solutions,  nevertheless  is  also  known  to 
produce,  by  long-continued  action,  chemical  effects  similar  to  those 
that  are  more  quickly  and  energetically  brought  about  by  the  action  of 
caustic  lime.  In  fact,  the  agricultural  effects  of  "  liming  "  are  only  in 
degree  different  from  those  produced  by  marling  with  finely  pulverized 
carbonate ;  and  in  nature  the  same  relation  is  strikingly  exemplified  in 
the  peculiarly  black  humus  that  is  characteristic  of  calcareous  lands, 
but  which  can  be  much  more  quickly  formed  under  the  influence  of 
caustic  lime  on  peaty  soils. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS,  389 

In  the  analysis  of  silicates  we  employ  caustic  lime  for  the  setting- 
free  of  the  alkalies  and  the  formation  of  easily  decomposable  silicates, 
by  igniting  the  mixture;  but  the  carbonate  will  slowly  produce  a  similar 
change,  both  in  the  laboratory  and  in  the  soils  in  which  it  is  constantly 
present.  This  is  strikingly  seen  when  we  contrast  the  analyses  of 
calcareous  clay  soils  of  the  humid  region  with  the  corresponding  non- 
calcareous  ones  of  the  same.  In  the  former  the  proportions  of  dis- 
solved silica  and  alumina  are  almost  invariably  much  greater  than  in  the 
latter,  so  far  as  such  comparisons  are  practicable  without  assured  absolute 
identity  of  materials.  That  is,  calcareous  clays  or  clay  soils  are  so  sure 
to  yield  to  the  analyst  large  precipitates  of  alumina,  that  experience 
teaches  him  to  employ  smaller  amounts  for  analysis  than  he  would  of 
non-calcareous  materials,  in  order  to  avoid  unmanageably  large  bulks  of 
aluminic  hydrate.  It  is  but  rarely  that  even  the  heaviest  non-calcareous 
soils  yield  to  the  acid  usually  used  in  soil  analysis  more  than  10  per 
cent,  of  alumina  ;  while  heavy  calcareous  clay  (prairie)  soils  commonly 
yield  between  13  and  20  per  cent.1  It  would  be  interesting  to  verify 
this  relation  by  artificial  digestions  of  one  and  the  same  clays  with 
calcic  carbonate  at  high  temperatures,  as  it  must  always  be  extremely 
difficult  to  insure  absolute  identity  of  all  other  conditions  in  natural 
materials. 

In  most  of  these  cases,  what  is  true  of  alumina  is  also  true  of  the 
soluble  silica.  But  since  the  latter  is  constantly  liable  to  be  dissolved 
out  by  solutions  of  carbonated  alkalies,  it  is  not  surprising  that  this 
relation  is  not  always  shown. 


Hydrate.  —  In  numerous  cases,  the  amount  of 
alumina  dissolved  in  analysis  is  greatly  in  excess  of  the  soluble 
silica,  so  as  to  force  the  conclusion  that  a  portion  of  the  latter 
must  be  present  in  a  different  form  from  that  of  clay  (  kaoli- 
nite)  ;  the  only  choice  being  between  that  of  complex  hydrous 
silicates  (none  of  which,  however,  could  contain  as  large  a  per- 
centage of  alumina  as  clay  itself)  and  aluminic  hydrate.  The 
latter  is  alone  capable  of  explaining  the  presence  of  more 
alumina  than  silica  in  easily  soluble  form;2  and  the  visible 
occurrence  of  "  gibhsite  "  and  "  bauxite  "  in  modern  forma- 

1  Report  of  the  Tenth  Census,  Vols.  5  &  6  ;  see  especially  the  analyses  of  soils 
from  Mississippi  and  Alabama.  Also  the  Reports  of  the  California  Experiment 
Station. 

-  Excepting  the  relatively  rare  minerals  of  the  Allophane,  Kollyrite,  and 
Miloshite  group. 


390 


SOILS. 


tions  renders  this  a  perfectly  simple  and  acceptable  explanation. 
Since  these  minerals  are  known  to  be  incapable  of  crystalli- 
zation, we  are  moreover  led  to  the  presumption  that  it  will  as  a 
rule  be  found  in  the  finest  portions  of  the  soil,  viz.,  in  the 
"  clay  "  of  mechanical  analysis. 

Some  illustrations  of  these  conditions  are  given  below,  for  soils  from 
Mississippi  and  California.  The  soluble  silica  being  all  assigned  to 
kaolinite,  the  rest  of  the  alumina  must  be  assumed  to  be  present  as 
hydrate,  since  no  other  compound  could  fulfil  the  stoichiometrical  re- 
quirements.1 The  table  therefore  shows  the  differences  between  the 
amounts  of  alumina  found  by  analysis,  and  those  assignable  to  kaolinite, 
calculated  to  the  mineral  bauxite — the  most  abundant,  as  well  as  the 
one  containing  the  medium  proportion  of  water,  among  the  three 
naturally  occurring  aluminic  hydrates. 

TABLE   SHOWING    EXCESS   OF    ALUMINA    OVER    SILICA    IN    SOILS  ;   CALCULATED    AS 

BAUXITE. 


Num- 
ber. 

Name  of  Soil. 

County. 

State. 

Total  solu- 
ble in  HC1. 

SiO.., 

Al.,O». 

Correspond- 
ing to 
Bauxite. 

Other 
Solu. 
Matters. 

*9S 

28  57 

3.6 

14.4 

346 

6.6 

86 

288 
676 
332 

Flatwoods  Clay  
Red  Volcanic  
Mojave  Desert  
Red  Foothill  

Pontotoc. 
Lake  .... 
Kern  .  .  . 

California. 

26.94 
41.00 
24.82 

5.0 
5-9 

"•3 

22.6 
9  2 

8.8 

8.75 

2I.QO 

6.10 

3.48 

2.0O 

5  <3 

7°S 
706 
573 

Red  Chaparral  
"            "     Subsoil.. 
Tulare  Plains  

Shasta.... 
Tulare.... 

'• 

28.75 
28.40 
29.27 

5-5 
4-7 
3-4 

14.4 

'7-4 
8.7 

12.  IO 

16.70 

7.20 

1.  12 
'   32 

ii.  16 

1004 
656 
S'7 
56' 

"  Slickens  "  Sed  
Brownish  Loam  

Butte  
Yuba  .... 
Butte  

• 

30.80 
22.23 
29.80 

8.0 

3-° 
4.8 

14.2 
10.4 

12.0 

9.20 

9.80 
9.80 

12  80 

'•95 
2.19 
4.42 

A    67 

563 
863 
861 

Sacramento  Alluvium. 
Red  Foothill  

Nevada  .. 

« 

23.46 
56.80 

2.7 

Il.O 

10.4 
36.4 

10.90 

33-6o 

4.58 

1.22 

It  is  apparent  from  this  table  that  if,  as  is  probable,  the  aluminic 
hydrate  accumulates  in  the  "  clay  "  of  the  analysis,  it  will  in  some  cases 
form  a  very  considerable  percentage  of  the  same,  and  detract  to  that 
extent  from  its  plastic,  adhesive  and  other  properties.  But  it  must  be 
remembered  that  the  assumption  upon  which  this  table  is  calculated, 
leaves  out  of  consideration  the  zeolitic  portion,  which  as  the  6th  column 
shows,  is  frequently  quite  large  as  measured  by  the  bases  found,  to 

1  Since  any  complex  zeolite  would  contain  less  alumina  than  kaolinite,  this 
assumption  more  than  covers  the  possible  zeolitic  alumina. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  391 

which  no  other  form  of  combination  can  be  assigned.  Since  some  of 
the  alumina  undoubtedly  takes  part  in  the  formation  of  such  zeolites, 
the  silica  must  to  that  extent  be  withdrawn  from  the  estimate  made  for 
kaolinite.  While  it  is  impossible  to  make  any  definite  numerical  al- 
lowance for  this  fact,  it  clearly  will  tend  in  many  cases  to  increase 
materially  the  amount  of  alumina  that  must  be  assigned  to  the  hydrate 
condition.  It  will  be  noted  that  in  most  cases  given,  the  alumina  per 
cent  is  rather  large. 

The  relatively  large  number  of  such  cases  shown  in  the  table 
for  California  soils  is  not  a  matter  of  accident ;  for  even  a  cur- 
sory glance  at  the  columns  of  analyses  of  California  (and 
Washington  and  Montana)  soils,  shows  that  the  cases  in 
which  the  alumina  exceeds  the  silica  in  amount  are  rather  pre- 
dominant, while  the  reverse  is  the  case  in  the  humid  region.1 
But  it  must  not  be  inferred  that  the  reverse  relation  is  not  also 
frequently  observed  even  in  the  arid  region ;  it  occurs  in  fact 
in  close  proximity  to  the  localities  where  some  of  the  most 
striking  instances  of  excess  of  alumina  over  soluble  silica  have 
been  found. 

Thus  Nos.  86 1  and  863  from  the  neighborhood  of  Grass  Valley, 
which  show  this  excess  most  strikingly,  occur  within  15  miles  of  local- 
ities which  show  almost  the  reversal  of  the  numbers  given  for  the  two 
former,  and  at  a  level  of  about  a  thousand  feet  lower.  It  would  seem, 
on  the  whole,  that  the  excess  of  alumina  occurs  most  frequently  in  con- 
nection with  soils  formed  from  eruptive  rocks ;  in  the  case  referred  to, 
from  volcanic  ash.  It  will  require  more  detailed  study  to  detect  the 
causes  of  these  marked  differences. 

Retention  of  So  I  it  bit-  Silica  in  Alkali  Soils, — It  is  somewhat  surprising 
that,  contrary  to  the  expectation  one  would  naturally  entertain,  the 
alkali  lands,  so  frequently  rich  in  the  carbonates  of  the  alkalies  that 
would  dissolve  free  silica,  on  the  contrary,  show  most  frequently  an 
excess  of  soluble  silica  over  alumina.  This  is  probably  to  be  explained 
from  the  very  liberal  opportunities  afforded  in  the  alkali  soils  for  the 
formation  of  complex  zeolitic  masses  by  the  retention  in  soil  of  the 
soluble  alkali  salts,  and  the  abundance  of  lime  always  present  in  them. 
As  already  stated,  we  usually  find  in  alkali  soils  a  very  large  proportion 

1  See  for  comparison  the  data  given  in  vols.  5  and  6  of  the  report  of  the  Tenth 
Census  of  the  United  States. 


392 


SOILS. 


of  both  alkaline  and  earthy  bases  in  acid-soluble  silicate  combinations. 
But  much  farther  research  is  needed  to  explain  fully  the  marked  dis- 
crepancies observed  in  this  respect  between  soils  not  only  occurring  in 
closely  contiguous  localities,  but  also  showing  marked  similarities  in 
their  general  composition. 

Ferric  Hydrate. — There  is  no  obvious  reason,  from  the 
chemical  standpoint,  why  iron,  that  is,  ferric  hydrate  or  iron 
rust,  should  be  more  abundant  in  the  soils  of  the  arid  regions, 
as  the  averages  given  in  the  table  suggest ;  moreover,  the  fact 
does  not  impress  itself  upon  the  eye,  since  the  orange  or  reddish 
tints  are  by  far  more  common  in  the  humid  than  in  the  arid 
regions  of  the  United  States  at  least.  The  California  average 
is  considerably  influenced  by  the  very  highly  ferruginous  soils 
from  the  foothills  of  the  Sierra  Nevada,  and  by  the  black 
(magnetite)  sand  so  commonly  present;  that  of  Oregon  by  the 
black,  highly  ferruginous  country  rock  (basalts),  from  which 
they  are  partly  derived.  The  average  for  Montana  is  not 
higher  than  that  of  three  states  of  the  humid  region,  and  less 
than  that  of  Kentucky.  We  might  imagine  a  cause  for  deple- 
tion of  iron  in  the  soils  of  the  humid  areas  in  the  frequency 
with  which  humid  moisture  and  high  temperature  will  during 
the  summers  concur  toward  the  bringing  about  of  a  reducing" 
process  in  the  soil,  which  by  getting  the  iron  into  proto-car- 
bonate  solution  would  make  it  liable  to  be  leached  into  the  sub- 
soil, as  is  frequently  the  case;  yet  the  resulting  "  black  gravel  " 
or  bog  ore,  in  its  various  forms,  is  of  not  infrequent  occurrence 
in  the  arid  regions  also.  A  constant  quantitative  difference  due 
to  climatic  conditions  does  not  appear  to  be  shown  by  the  data 
thus  far  at  command,  but  the  finer  distribution  of  the  ferric 
hydrate  in  the  humid  temperate  as  well  tropical  regions  is 
obvious  to  the  observer,  from  the  frequent  redness  of  humid 
and  tropical  soils. 

Manganese. — An  unexpected  and  apparently  well-defined 
contrary  relation  appears  to  be  shown  as  regards  the  related 
metal  manganese;  the  average  percentage  of  which  is  in  all 
cases  less  in  the  arid  than  in  the  humid  region.  The  cause  of 
this  relation  is  altogether  obscure;  it  is  too  frequent  to  be  ac- 
cidental. 

Phosphoric  Acid. — As  regards  that  highly  important  soil 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


393 


ingredient,  phosphoric  acid,  the  indication  in  the  table  that 
there  is  no  characteristic  difference  in  the  average  contents  in 
soils  of  the  arid  and  humid  regions,  respectively,  is  doubtless 
correct.  This  substance  is  so  tenaciously  retained  by  all  soils 
that  there  is  no  obvious  reason  why  there  should  be  any  ma- 
terial influence  exerted  upon  its  quantity  by  leaching,  or  by 
any  of  the  differences  in  the  process  of  weathering  that  are 
known  to  exist  between  the  two  climatic  regions.  Moreover, 
it  is  apparent  that  the  average  for  the  arid  region  is  made  up 
out  of  very  widely  divergent  figures;  that  of  California  excep- 
tionally low  (lower  than  any  of  those  for  the  states  of  the 
humid  regions),  while  those  for  Washington  and  Montana  are 
exceptionally  high.  The  latter  is  due  to  country  rocks 
("basalts")  showing  abundance  of  microscopic  crystals  of 
apatite,  which  in  some  cases  raise  the  contents  of  the  soils  in 
phosphoric  acid  to  nearly  twice  the  average  given  for  the 
states. 

The  forecast  that  for  most  California  soils,  fertilization  with 
phosphates  is  of  exceptional  importance,  has  already  been 
abundantly  confirmed  by  cultural  experience.  Few  definite 
data  are  as  yet  available  from  other  arid  states,  where  fertil- 
ization is  thus  far  sporadic  and  unsystematic.  But  it  is  pre- 
dicable  that  in  view  of  the  presence  of  an  excess  of  lime  carbon- 
ate in  the  arid  soils,  and  the  unfavorable  effect  of  this  com- 
pound on  the  rapid  solubility  of  tricalcic  phosphate  demon- 
strated by  Schloesing,  Jr.,1  by  Bottcher  and  Kellner 2  and 
Naganka,:i  fertilization  with  readily  available  phosphate  fertil- 
izers will  be  found  necessary  among  the  first,  all  over  the  arid 
region,  especially  in  view  of  the  scarcity  of  humus  in  arid  soils. 

A  curious  instance  of  the  effects  of  continued  warm  maceration  in 
rock  decomposition  is  afforded  by  the  highly  ferruginous  soils  derived 
from  the  black  basaltic  lavas  of  the  Hawaii  Islands.  These  lavas,  like 
the  basalt  sheet  of  the  Pacific  Northwest,  contain  a  large  amount  of 
crystallized  phosphate  minerals,  notably  apatite  and  vivianite.  A  cor- 
respondingly large  proportion  of  phosphoric  acid  is  found  in  the  soils 

1  Ann.  Sci.  Agronomique,  tome  i,  1899. 

3  Landw.  Presse,  1900,  No.  52  ;  ibid.  1901,  Nos.  23  and  24. 

"  Hull.  Univ.  Tokyo,  Vol.  6,  N'o.  3.  Production  was  diminished  to  less  than  one 
half  when  lime  was  used  with  bone  meal,  and  actual  assimulation  of  phosphoric 
acid  to  one  fifth. 


394 


SOILS. 


derived  from  these  rocks,  up  to  nearly  two  per  cent.1  But  almost  the 
entirety  if  this  substance  is  present  in  the  form  of  an  insoluble,  basic 
iron  compound,  difficultly  soluble  even  in  acids,  and  rendering  it  wholly 
unavailable  to  vegetation.  So  that  actually  the  most  pressing  need  of 
most  of  these  soils  is  phosphate  fertilization.  The  same  is  probably 
true  of  some  of  the  highly  ferruginous  soils  of  California  and  of  the 
Cotton  States. 

Sulfuric  Acid. — From  the  absence  of  the  leaching  process 
in  the  soils  of  the  arid  region,  we  should  expect  that  sulfates 
would  be  more  abundant  in  them  than  in  the  soils  of  the  humid. 
This  is  certainly  true  in  the  case  of  the  alkali  soils,  which  are 
characteristic  of  the  regions  of  deficient  rainfall.  See  below, 
chapter  22. 

Hence  the  showing  made  in  the  general  table,  indicating  that  sulfates 
are  equally  abundant  in  the  soils  of  the  humid  than  in  those  of  the  arid 
regions,  is  surprising  in  view  of  the  efflorescences  of  alkali  sulfates  so 
frequently  observed  in  the  latter.  This  is  obviously  due  to  the  fact 
that  the  majority  of  such  alkali  soils  has,  on  account  of  their  local  nature 
and  usually  heavy  lime  content,  been  excluded  from  the  comparison  ; 
which  otherwise  would  have  made  a  very  different  showing. 

Potash  and  Soda. — The  compounds  of  the  alkali  metals 
potassium  and  sodium,  being  on  the  whole  much  more  soluble 
in  water,  even  without  the  concurrence  of  carbonic  acid,  than 
those  of  calcium  and  magnesium,  the  leaching  process  that 
creates  such  pronounced  differences  in  the  case  of  the  two 
earths  must  affect  the  alkali  compounds  very  materially. 
Comparison  of  the  soils  of  the  two  regions  in  this  respect 
shows,  indeed,  very  great  differences  in  the  average  contents 
of  potash  and  soda.  For  potash  the  ratio  is  .216  to  .670  per 
cent,  on  the  general  average,  and  .187  to  .670  per  cent.,  in  the 
average  by  states;  for  soda,  .140  per  cent,  to  .350  per  cent, 
on  the  general  average,  and  .no  per  cent,  to  .420  per  cent,  in 
the  average  by  states.  For  both,  therefore,  the  general  aver- 
age ratio  is  as  one  to  between  three  and  four  for  the  humid  as 
against  the  arid  region. 

It  is  curious  that  an  approximation  to  the  ratio  of  one  to 

1  See  table,  chapter  19,  p.  256. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


395 


two,  or  somewhat  less,  is  maintained  in  the  average  propor- 
tion of  soda  to  potash  in  both  regions ;  but  this  does  not  by  any 
means  hold  good  in  detail,  very  high  potash-percentages  being 
often  accompanied  by  figures  for  soda  very  much  below  the 
above  ratio.  This  is  the  result  of  an  important  difference  in 
the  chemical  behavior  of  the  two  alkalies,  which  has  already 
been  alluded  to  in  connection  with  the  discussion  of  the  zeo- 
lites. (See  chapter  3,  p.  38). 

The  process  of  "  kaolinication,"  being  that  by  which  clays 
are  formed  out  of  feldspathic  minerals  and  rocks  such  as 
granite,  syenite,  trachyte,  etc.,  results  in  the  simultaneous  form- 
ation of  solutions  of  carbonates  and  silicates  of  potash  and 
soda.  These  coming  in  contact  with  the  corresponding  com- 
pounds of  lime  and  magnesia,  also  common  products  of  rock 
decomposition,  are  partly  taken  up  by  the  latter,  forming 
complex,  insoluble,  hydrous  silicates  (zeolites).  In  these, 
however,  potash  whenever  present  takes  precedence  of  soda; 
so  that  when  a  solution  of  a  potash  compound  is  brought  in 
contact  with  a  zeolite  containing  much  soda,  the  latter  is  par- 
tially or  wholly  displaced  and,  being  soluble,  tends  to  be  washed 
away  by  the  rainfall  into  the  country  drainage.  Hence  potash, 
fortunately  for  agriculture,  is  tenaciously  held  by  soils,  while 
soda  accumulates  only  where  the  rainfall  or  drainage  is  in- 
sufficient to  effect  proper  leaching,  and  in  that  case  manifests 
itself  in  the  formation  of  what  is  popularly  known  as  "  alkali 
soils;"  namely  those  in  which  a  notable  amount  of  soluble 
salts  exists,  and  is  kept  in  circulation  by  the  alternation  of  rain- 
fall and  evaporation,  the  latter  causing  the  salts  to  accumulate 
at  the  surface  and  to  manifest  themselves  in  the  form  of  saline 
crusts  or  efflorescenses.  Alkali  lands  are  a  characteristic 
feature  of  all  regions  of  scanty  rainfall,  and  arc  found  more  or 
less  on  all  the  continents.  The  substances  composing  the  alkali 
salts  are  retained  not  only  in  their  soluble  form,  but  by  their 
continued  presence  influence  profoundly,  in  several  ways,  the 
processes  of  soil  formation.  A  more  detailed  discussion  of 
this  important  subject  is  given  in  chapters  22  and  23. 

Arid  Soils  arc  Rich  in  Potash. — One  of  the  most  important 
practical  conclusions  flowing  from  the  comparison  of  the  pot- 
ash contents  of  the  humid  and  arid  soils  respectively  is  that 
while  in  the  former,  potash  is  usually  among  the  firs'  sub- 


396  SOILS. 

stances  to  be  supplied  by  fertilization  when  production  lan- 
guishes, in  the  arid  regions  it  will  as  rule  come  last  in  order 
among  the  three  ingredients  commonly  so  furnished.  Aside 
from  the  water-soluble  potash  salts  always  forming  part  of 
the  salts  of  the  alkali  lands  proper,  which  in  many  cases  will 
alone  hold  out  for  many  years  under  the  demands  of  cultiva- 
tion,1 they  rarely  contain  much  less  than  one  per  cent,  of  acid- 
soluble  potash;  occasionally  rising  as  high  as  1.8  per  cent. 
That  in  such  lands  potash-fertilization  is  uncalled-for  and  in- 
effective, hardly  requires  discussion ;  while  on  the  other  hand, 
phosphates  are  commonly  required  for  full  production  after 
ten  or  fifteen  years  of  cultivation  without  returns.  Nitrogen 
usually  comes  next  in  order,  but  sometimes  is  the  first  need. 

The  constant  indiscriminate  purchase  and  use  of  all  three  ingredients, 
so  urgently  recommended  by  fertilizer  manufacturers  because  of  their 
success  in  the  humid  Eastern  States,  is  therefore  very  poor  economy  for 
the  farmers  of  the  arid  region.  Excepting  cases  of  very  intense  culture, 
e.g.  of  vegetables  or  berries,  the  use  of  potash  salts  is  but  rarely  remuner- 
ative, and  therefore  uncalled-for,  in  arid  soils  for  a  number  of  years. 

Humus. — The  figures  shown  in  the  table  for  the  average 
humus-percentages  in  the  soils  of  the  two  regions  do  not  ade- 
quately represent  the  very  important  differences  actually  ex- 
isting; partly  because  of  the  inadequate  number  of  determina- 
tions made  by  the  same  method  (Grandeau's),  partly  because 
of  the  differences  in  the  composition,  and  especially  in  the 
nitrogen-content  of  this  substance,  which  render  direct  com- 
parison delusive.  A  detailed  discussion  of  the  marked  differ- 
ences existing  between  the  humus  of  arid  and  humid  soils  in 
this  respect  has  already  been  given  (chapter  8,  p.  135)  ;  show- 
ing that  the  high  nitrogen-percentage  in  the  arid  humus  prob- 
ably compensates  largely  the  lower  humus-percentage,  while 
rendering  nitrification  more  rapid,  because  the  oxygen  is  not 
consumed  by  overwhelming  amounts  of  carbon  and  hydrogen ; 
which,  as  is  already  known,  take  precedence  of  nitrogen  in  the 
oxidation  of  humus  substances.  Nitrates  are  almost  always 

1  In  the  light  alkali  lands  of  the  southern  California  Experiment  Substation  at 
Chino,  the  average  content  of  water-soluble  potash  in  ten  acres  amounts  to  the 
equivalent  of  1,200  pounds  of  potash  sulphate  per  acre.  Outside  of  this  the  acid- 
soluble  potash  of  the  soil  is  .95°  0.,  equal  to  38,00x3  pounds  per  acre-foot. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


397 


more  abundant  in  the  soils  of  the  arid  region  than  in  those  of 
the  humid,  sometimes  to  the  extent  of  influencing  injuriously 
the  quality  of  certain  crops,  such  as  tobacco  and  sugar  beets. 
Nevertheless,  nitrogen  is  ordinarily,  in  the  arid  region,  the  sub- 
stance requiring  replacement  next  to  phosphoric  acid.  And 
when  considered  in  connection  with  the  small  humus-content, 
so  liable  to  burning-out,  this  places  green-manuring  icitli  le- 
guminous plants  among  the  first  and  most  vital  improvements 
to  be  employed  there. 

The  Transition  (semi-humid  or  semi-arid)  Region. — The 
sloping  plains  country  lying  between  the  Rocky  Mountains 
and  the  Mississippi,  quite  arid  at  the  foot  of  the  mountains, 
but  with  rainfall  increasing  more  or  less  regularly  to  eastward, 
form  a  transition-belt  between  the  arid  and  humid  region  of 
which  but  a  small  portion  has  been  systematically  studied  in 
respect  to  its  soil  formations.  The  analyses  made  of  soils  of 
the  two  adjacent  states  of  Minnesota  and  North  Dakota,  have 
been  placed  in  the  general  table  (p.  3/7)  to  show  how  far  in 
their  general  relations  their  soils  correspond  to  the  generaliza- 
tions deduced  from  the  comparison  of  the  decidedly  arid  and 
humid  soil  areas  chiefly  represented  in  the  table.  Although  it 
has  not  been  possible,  for  lack  of  detailed  data,  to  eliminate 
the  soils  originating  from  calcareous  formations,  it  will  be 
seen  that  those  of  semi-arid  Dakota  differ  from  those  of  more 
humid  Minnesota,  almost  throughout,  as  would  be  anticipated 
from  the  studies  of  the  extremes,  given  in  this  chapter. 


CHAPTER  XXI. 

SOILS  OF  ARID  AND  HUMID  REGIONS  (Continued). 

SOILS   OF  THE  TROPICS. 

WITHIN  the  ordinary  limits  of  atmospheric  temperatures, 
and  in  the  presence  of  adequate  moisture,  chemical  processes 
active  in  soil-formation  are  intensified  by  high  and  retarded  by 
low  temperatures,  all  other  conditions  being  equal.  We  can 
usually  artificially  imitate,  and  produce  in  a  short  time  by  the 
application  of  relatively  high  temperatures,  most  of  the  chemi- 
cal changes  that  naturally  occur  in  soil-formation.  While  it  is 
true  that  the  changes  of  temperature  are  nearly  as  great  in  the 
tropical  as  in  the  temperate  climates,  these  changes  all  occur 
at  a  higher  level  and  within  the  limits  favoring  bacterial  and 
fungous  action. 

This  being  true  we  should  expect  that  the  soils  of  tropical 
regions  should,  broadly  speaking,  be  more  highly  decomposed 
than  those  of  the  temperate  and  frigid  zones,  and  that  the 
intensified  processes  continue  currently.  This  fact  has  not 
been  as  fully  verified  as  might  be  desirable,  by  the  direct 
comparative  chemical  examination  of  corresponding  soils  from 
the  several  regions,  owing  to  the  want  of  uniformity  in 
methods  and  the  fewness  of  such  investigations  in  tropical 
countries.  Yet  the  incomparable  luxuriance  of  the  natural  as 
well  as  artificial  vegetation  in  the  tropics,  and  the  long  duration 
of  productiveness  that  favors  so  greatly  the  proverbial  easy- 
going ways  and  slothfulness  of  the  population  of  tropical 
countries,  offers  at  least  presumptive  evidence  of  the  practical 
correctness  of  this  induction. 

In  other  words,  the  fallowing  action,  which  in  temperate 
regions  takes  place -with  comparative  slowness,  necessitating 
the  early  use  of  fertilizers  on  an  extensive  scale,  is  much  more 
rapid  and  effective  in  the  hot  climates  of  the  equatorial  rainy 
belt;  thus  rendering  currently  available  so  large  a  proportion 

398 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  399 

of  the  soil's  intrinsic  stores  of  plant-food,  that  the  need  of 
artificial  fertilization  is  there  largely  restricted  to  those  soils 
of  which  the  parent  rocks  were  exceptionally  deficient  in  the 
mineral  ingredients  of  special  importance  to  plants,  that  or- 
dinarily form  the  essential  material  of  fertilizers.  Quartzose, 
magnesian,  and  other  soils  resulting  from  the  decomposition 
of  "  simple  "  rocks  will,  of  necessity,  be  poor  in  plant-food 
everywhere. 

Humus  in  Tropical  soils. — Another  inference  from  the  cli- 
matic conditions  of  the  tropics  is  that  the  properly  tropical 
soils  are  likely  to  be  rich  in  humus,  as  a  result  of  the  luxuriant 
vegetation  which  in  the  decay  of  its  remnants  must  leave  abun- 
dant humic  residues.  This  seems  to  be  generally  verified 
wherever  the  interval  between  rainy  seasons  is  not  too  long; 
for  otherwise,  under  the  great  and  constant  heat  of  the  tropics 
a  rapid  burning-out  of  the  humus,  such  as  is  known  to  occur 
in  the  arid  regions,  must  also  take  place.  A  good  example 
illustrating  the  intertropical  regime  as  regards  humus  is  given 
in  the  table  in  chapt.  8,  p.  137,  showing  the  humus-content  of 
some  Hawaiian  soils.  Both  are  of  the  same  order  as  in  the 
soils  of  the  temperate  humid  region,  though  the  nitrogen-con- 
tent evidently  can,  consistently  with  productiveness,  range 
lower  than  has  thus  far  been  observed  in  temperate  climates. 
This  again  forms  a  striking  contrast  with  the  soils  of  the  arid 
regions. 

It  is  greatly  to  be  regretted  that  not  even  approximate  de- 
terminations of  the  organic  matter,  much  less  of  the  humus- 
substance  proper,  have  been  made  by  any  of  those  who  have 
analyzed  tropical  soils;  excepting  those  made  of  Hawaiian 
soils  at  the  California  Experiment  Station. 

The  "  loss  by  ignition  "  is  of  courst-  always  very  largely 
water,  mostly  referrible  to  ferric  hydrate  and  clay  substance, 
the  latter  presumably  essentially  in  the  form  of  kaolinite. 
\Yhen,  therefore,  ferric  oxid  and  alumina  have  been  deter- 
mined, we  may  approximate  to  the  amount  of  total  organic 
matter  by  making  allowance  for  ferric  hydrate  at  the  rate  of 
about  14%  of  the  ferric  oxid.  for  kaolinite  at  that  of  34.^2'  o 
of  the  alumina  found.  Deducting  these  amounts  of  water 
from  the  total  "  loss  by  ignition,"  we  may  obtain  at  least  an 
approximate  idea  of  the  organic  matter,  and  the  probable 


400  SOILS. 

availability  of  the  nitrogen  determined  by  the  analysis.  See 
chapter  19,  p.  357. 

While  the  continuous  heat  and  moisture  of  the  tropics  concur 
toward  rapid  rock-decomposition,  it  must  be  remembered  that 
the  copious  rainfall  is  equally  conducive  to  an  intense  leaching 
effect.  Striking  examples  of  this  action  occur  in  the  Hawaiian 
Islands,  in  the  highly  ferruginous  soils  resulting  from  the 
decomposition  of  the  black  (pyroxenic  and  hornblendic)  lavas 
that  are  so  characteristic  of  the  volcanic  effusions  of  that 
region.  The  soils  formed  from  these  rocks  are  sometimes  so 
rich  in  ferric  hydrate  (iron  rust)  that  they  might  well  serve 
as  iron  ores  elsewhere.  But  these  soils  are  very  unretentive, 
and  though  very  productive  at  first  they  are  soon  exhausted, 
the  abundant  rains  having  sometimes  deprived  them  of  almost 
every  vestige  of  lime,  and  of  most  of  the  potash  contained  in 
the  original  rock.  At  the  same  time  the  abundant  phosphoric 
acid  of  the  original  rock  has  been  reduced  to  almost  total 
unavailability  by  combination  with  ferric  oxid,  just  as  in  the 
case  of  the  bog  ore  of  the  temperate  climates ;  so  that  phosphate 
fertilization  is  urgently  needed  in  these  lands,  though  showing 
high  percentage  of  phosphoric  acid.  (Chapt.  19,  p.  356.) 

Soils  highly  colored  by  ferric  hydrate  occur  rather  fre- 
quently in  the  tropics,  and  have  received  the  general  name  of 
"  laterite  "  soils.  Curiously  enough,  the  intense  reddish  tint 
mostly  shown  in  these  soils,  and  which  is  emphasized  in  the 
"  terra  roxa  "  of  the  Brazilians,  and  the  general  "  red  "  aspect 
of  Madagascar,  and  of  the  Malabar  and  Bengal  coasts,  is  by 
no  means  always  accompanied  by  markedly  high  percentages 
of  iron  oxid ;  but  the  latter  is  very  finely  diffused,  so  as  to  be 
very  effective  in  coloration.  The  plant-food  percentages  of 
tropical  soils  are  generally  quite  low,  so  that  in  the  temperate 
humid  regions  such  lands  would  be  adjudged  to  be  rather  poor. 
Yet  they  mostly  prove  quite  productive  and  lasting,  even  with- 
out fertilization. 

This  is  doubtless  to  be  explained  by  the  continuous  and  rapid  rock 
and  soil-decomposition  which  goes  on  under  tropical  climatic  conditions, 
already  alluded  to ;  so  as  to  supply  enough  available  plant-food  for  the 
demands  of  each  season's  vegetation,  analogously  to  the  proverbial 
"  nimble  penny."  This  is  supplemented  also  by  the  rapid  decay  and 
eaching-out  of  the  ash  ingredients  of  the  rapidly  decaying  and  dying 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


401 


vegetation.  Nitrification  must  likewise,  of  course,  be  very  active  under 
the  continual  heat  and  moisture,  and  the  humus  formed  under  these 
circumstances  is  likely  to  be  quite  poor  in  nitrogen.  On  this  latter 
point,  however,  definite  data  are  almost  wholly  wanting. 

Investigations  of  Tropical  Soils. — The  most  extended  chemi- 
cal investigations  of  properly  tropical  soils  have  been  made  by 
Wohltmann  in  his  investigations  of  the  soils  of  India,  German 
Southwest  and  Southeast  Africa,  and  Samoa;1  and  by 
Miintz  and  Rousseaux  of  soils  collected  under  Government 
auspices  in  Madagascar.  Leather,  Bamber  and  Mann  have  also 
analyzed  a  large  number  of  soils  of  India.  But  we  find  in 
many  of  these  cases  a  failure  to  specify  distinctly  the  local 
climatic  conditions,  and  even  the  depth  to  which  the  samples 
have  been  taken;  so  that  the  investigator  is  obliged  to  examine 
laboriously  the  local  climates,  and  especially  the  amount  and 
distribution  of  rainfall,  before  being  enabled  to  discuss  intelli- 
gently the  data  given.  Even  Wohltmann,  in  his  discussion  of 
North  African  and  Saharan  soils,  classes  these  distinctly  arid 
types  among  the  tropical  ones. 

.Again,  the  dry  seasons  intervening  between  the  tropical 
rains,  varying  in  length  and  from  locality  to  locality,  obscure 
somewhat  the  relations  of  the  soils  to  the  climatic  conditions. 
Under  the  lee  of  mountains,  even  of  slight  altitude,  we  find 
xerophytic  (arid-land) vegetation,  as  has  been  noted  by  many 
observers  in  Brazil,  even  near  the  Amazon;  in  Hawaii,  in 
Jamaica,  and  in  Madagascar.  Unless,  therefore,  a  close  dis- 
crimination is  exercised  by  field  observers,  many  contradictory 
results  will  appear  in  analyses  of  soils  of  inter-tropical  coun- 
tries. This  is  naturally  the  case  in  India,  where  the  topo- 
graphic surface  conformation  and  seasonal  climatic  conditions 
are  so  complicated  and  contrasted.  On  the  whole,  the  results 
obtained  in  Samoa,  Kamerun  and  Madagascar  seem,  of  those 
available,  to  be  the  most  characteristic  of  true  tropical  condi- 
tions. In  comparing  these  with  the  soils  of  low  plant-food 
percentages  in  the  temperate  humid  region  (see  chapter  19. 
p.  352),  it  must  be  remembered  that  those  mentioned  as  being 
productive  are  so  by  virtue  of  great  depth  and  relatively  high 

1  Samoa  Krkundung,  by  F.  Wohltmann,  Kolonial-Wirthsch,  Komitee,  Berlin, 
1904. 

26 


4O2 


SOILS. 


proportions  of  lime;  while  in  the  tropics,  the  intense  leaching 
process  prevents  lime  from  reaching  any  high  absolute  or 
relative  percentages,  save  where  limestone  formations  prevail. 
Moreover,  the  mode  of  preparation  of  the  soil  extracts  for 
analysis  by  Wohltmann,  and  by  Miintz  and  Rousseaux,  differ 
so  widely  from  that  forming  the  basis  of  discussion  of  soil-com- 
position in  this  volume,  that  it  becomes  necessary  to  make 
separate  allowances  in  each  case ;  since  some  of  the  ingredients, 
phosphoric  acid,  lime  and  magnesia,  are  fully  dissolved  by 
the  weaker  treatments,  while  others, — e.  g.,  potash — are  not, 
and  are  therefore  not  directly  comparable  with  the  data  ob- 
tained in  the  writer's  work.  The  analyses  made  in  India  by 
Leather  and  others  have  apparently  been  made  substantially 
in  accordance  with  the  author's  methods  and  may  be  considered 
directly  comparable. 

SOILS  OF  SAMOA  AND  KAMERUN. 

Wohltmann  has  investigated  the  soils  of  Samoa,  notably 
those  of  the  main  island  of  Upolu,  under  the  auspices  of  the 
German  "  Kolonial-Wirthschaftliche  Komitee  "  in  1903,  and 
gives  the  results  of  his  observations  and  analyses  in  a  report 
published  at  Berlin  in  1904.  The  analyses  are  quite  numerous, 
but  unfortunately  are  made  by  a  special  method  which  renders 
them  only  partly  comparable  with  those  of  any  other  analyst. 

Wohltmann's  method  is  this :  "  450  grams  of  fine  earth  (below  2 
millimeters  diameter)  is  treated  for  48  hours  with  i-^-  liters  of  cold 
chlorhydric  acid  of  1.15  density.  Another  portion,  designed  for  a  fuller 
determination  of  potash,  is  treated  for  one  hour  with  the  same  acid, 
boiling  hot.  Potash  was  determined  in  both  soil  extracts ;  the  hot 
extract  gave  from  one-third  to  twice  the  amount  obtained  in  the  cold 
extraction."  l 

Wohltmann  justifies  this  method  by  the  statement  that  it  has  yielded 
him  results  more  nearly  in  accord  with  experience  than  any  other  tried, 
both  with  tropical  and  European  soils. 

Under  these  conditions  only  a  few  of  the  determinations  in  Wohlt- 
mann's analyses  are  directly  comparable  with  those  upon  which  the  discus- 

1  Wohltmann  states  that  the  hot  extraction  sometimes  yielded  as  muck  as  five 
times  more  than  the  cold ;  but  no  such  case  appears  in  his  reports  on  Samoa  and 
Kamerun. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


403 


sions  in  this  volume  have  been  based.  The  figures  for  nitrogen  and 
phosphoric  acid  may  be  assumed  to  be  fully  comparable  ;  that  of  lime  will 
in  general  represent  fully  only  that  which  is  present  in  the  forms  of 
carbonate,  sulfate  and  humate,  and  a  part  of  that  existing  in  zeolitic  or 
hydrous  silicate  form.  Of  the  two  potash  determinations  only  the  one 
made  in  hot  extraction  will  be  even  remotely  comparable,  being  pro- 
bably at  least  30%  lower  than  would  have  been  obtained  by  the  writer's 
method. 

Even  thus,  however,  Wohltmann's  results  are  highly  in- 
structive. He  gives  the  following  summary  of  his  mode  of 
interpreting  such  analyses : 


Very  rich. 

Good. 

Inadequate, 

Potash  

.2 

.1 

.CK 

Urne  and  Magnesia  

I.O 

•4 

.07 

Phosphoric  acid  

2 

.1 

.06 

Nitrogen  

2 

i 

.o<; 

It  will  be  observed  that  the  figures  of  this  table  differ  ma- 
terially only  'in  the  matter  of  potash  from  those  given  in  chap- 
ter 19,  p.  354;  for  the  latter  substance  they  would  have  to  be 
multiplied  by  from  2  to  4,  according  to  the  lime-content  and 
other  conditions. 

With  tliis  understanding  a  number  of  Wohltmann's  analyses 
of  soils  from  Samoa  and  Kamerun  are  given  below,  the  pot- 
ash determinations  made  with  hot  acid  being  placed  in  par- 
entheses after  the  other. 


of  Sa  moan  Islands.  —  A  discussion  of  these  analyses  shows,  from 
the  writer's  point  of  view,  a  very  low  content  of  potash  and  lime,  with 
the  peculiarity  trnt  both  are  somewhat  higher  at  the  depth  of  a  meter 
than  in  the  surface  ten-inches.  This  is  probably  to  be  accounted  for 
from  the  very  high  content  of  organic  matter  (humus),  which  is  apparent 
from  the  high  "  loss  by  ignition,"  a  very  large  proportion  of  which  must 
be  credited  to  the  burning  of  the  organic  matter.  That  this  humus 
reaches  to  the  lowest  depths  examined,  is  clear  from  the  nitrogen-con- 
tent given  for  these  samples.  Wohltmann,  whose  estimate  of  these 
soils  agrees  in  most  respects  with  the  writer's,  attributed  to  them  a  very 
satisfactory  nitrogen-content.  This  would  be  true  of  the  total  ;  but  as 


404 


SOILS. 


O    •*    «    ro  c*       O       O    «*}  "* 


a    JJ 


g§ 
82. 


2.>   S, 


oW 
E  « 


(23Sfa<35r^'h:'' 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


405 


he  has  not  determined  either  the  true  humus  or  its  nitrogen-content,  it 
remains  uncertain  whether  or  not  a  sufficiency  is  in  an  available  form, 
and  whether  their  case  may  not  be  like  that  of  the  Hawaiian  soil  men- 
tioned above  (chapter  19,  p.  362),  in  which  despite  10%  of  humus  and 
.17%  of  nitrogen,  the  land  was  found  to  be  nitrogen-hungry.  Again, 
as  regards  the  phosphoric  acid,  which  Wohltmann  considers  satisfactory 
to  high,  it  is  questionable  to  what  extent  it  is  rendered  unavailable  by 
the  very  high  content  of  ferric  hydrate.  We  are  thus  left  in  some  un- 
certainty as  to  the  real  manurial  requirements  of  the  Samoan  soils, 
which  doubtless  represent  very  closely  also  those  of  Tutuila,  the  chief 
American  island  of  the  group. 

It  is  probable  that  for  crops  requiring  so  much  potash  as  do  the 
banana  and  cacao  trees,  potash  is  the  first  need  when  they  cease  to 
produce  well  on  these  soils. 

Soils  of  Kamerun. — In  the  soils  of  Kamerun,  also  analyzed  by 
Wohltmann,  and  of  which  two  are  placed  alongside  of  those  of  Samoa, 
it  is  at  once  seen  that  the  materials  from  which  they  have  been  formed 
are  richer  in  both  potash  and  lime  than  the  parent  rocks  of  the  Samoan, 
and  not  quite  so  rich  in  iron.  They  are  also  very  rich  in  organic 
matter,  evidently  down  to  the  depth  of  a  meter,  as  are  those  of  Samoa. 
It  is  probably  due  to  the  high  humus-content  that  these  soils,  washed 
as  they  have  been  by  the  second-highest  rainfall  in  the  world  (about  35 
feet  annually)  have  not  been  as  thoroughly  leached  as  have  been  those 
of  the  Brahmaputra  valley.  The  annual  rainfall  of  Samoa  is  only  from 
nine  to  eleven  feet  on  the  lower  levels,  but  ranges  as  high  as  18  feet  at 
higher  elevations. 

It  is  noticeable  that  in  most  of  these  true  tropical  soils  the 
content  of  magnesia  is  considerably  above  that  of  lime;  a  fact 
readily  intelligible  from  the  more  ready  solubility  of  lime  in 
carbonated  water.  It  is  hardly  doubtful  that  this  dispropor- 
tion will  in  many  cases  explain  a  lack  of  thriftincss,  which 
could  be  effectually  remedied  by  a  simple  application  of  lime 
or  marl,  without  resorting  to  the  more  costly  fertilizers. 

THE  SOILS   OF    MADAGASCAR. 

The  soils  of  the  island  of  Madagascar  have  been  analyzed  to 
the  number  of  about  500  by  Miintz  and  Rousseaux.  under  the 
auspices  of  the  French  government.1  So  large  a  number  of 

1  Annales  de  la  Science  Agronomique,  tome  icr,  1901,  fasicules  i,  2,  3. 


406  SOILS. 

analyses  should  give  a  very  full  understanding  of  the  agricul- 
tural capacity  and  adaptation  of  so  comparatively  limited  an 
area ;  unfortunately,  we  are  here  again  confronted  by  more  or 
less  imperfect  data  accompanying  the  samples  collected  by 
government  agents,  and  by  the  use  of  an  analytical  method 
different  from  those  of  all  other  nations,  and  hence  incom- 
mensurable except,  as  in  the  case  of  Wohltmann's  method,  in 
regard  to  certain  ingredients. 

The  French  chemists  use  nitric  instead  of  chlorhydric  acid; 
cold  for  phosphoric  acid  and  lime,  boiling-hot  for  five  hours 
for  potash ;  considering  the  remainder  as  of  no  practical  import- 
ance. Since  nitric  acid  is  in  general  much  less  incisive  than 
chlorhydric  in  its  solvent  power,  comparison  with  the  analyses 
made  by  other  nations  becomes  difficult.  As  in  the  case  of 
Wohltmann,  magnesia,  lime,  and  phosphoric  acid  may  be  con- 
sidered to  be  quite  thoroughly  extracted  by  the  treatment; 
while  extraction  of  possibly  available  potash  is  doubtless  very 
incomplete.  On  the  whole,  however,  the  estimates  of  soil- 
fertility  based  on  percentages  is  very  nearly  the  same  as  those 
assigned  by  Wohltmann  in  the  table  given  above.  Like 
Wohltmann,  they  emphasize  the  axiom  that  the  same  percent- 
age-gauge of  fertility  cannot  be  applied  in  the  tropics  as  in  the 
temperate  zones. 

General  Character  of  the  Island. — The  island  of  Madagascar, 
lying  between  the  nth  and  25th  degrees  of  south  latitude,  is 
quite  mountainous  in  its  central  and  eastern  portion,  where 
the  coast  falls  off  pretty  steeply  into  the  sea,  leaving  only 
a  narrow  coast  belt  of  properly  agricultural  land  in  the 
lower  valleys  and  at  the  mouth  of  the  torrential  streams. 
The  mountains  rise  at  one  point  to  the  height  of  nearly  10,000 
feet.  The  western  portion  of  the  Island  is  much  less  broken, 
has  much  plateau  land  with  low  intersecting  ranges  and 
streams  of  moderate  fall,  with  considerable  alluvial  lands  near 
the  coast.  The  rocks  are  almost  throughout  gneisses  and 
mica-schists,  which,  as  heretofore  stated  (chapter  4,  p.  51), 
form  mostly  poor  soils.  There  are  a  few  areas  of  eruptive 
rocks  and  tertiary  calcareous  deposits,  and  on  these  the  lands 
are  much  more  thrifty.  The  rocks  and  red  soils  of  the  central 
mass,  however,  extend  seaward  almost  everywhere. 

The  rainfall  is  high  on  the  east  side,  where  the  moisture  of 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  407 

the  southeast  trade  winds  is  first  condensed,  the  precipitation 
reaching  ten  to  twelve  feet  (120  to  144  inches)  annually. 
The  western  portion  is  relatively  dry,  but  rains  fall  more  or  less 
throughout  the  year ;  while  in  the  eastern  and  central  moun- 
tainous part  there  is  a  distinct  subdivision  into  a  wet  and  a  dry 
season.  Here,  while  the  rivers  are  largely  torrential,  many 
large  fertile  valleys  have  been  created  by  the  heavy  denudation 
of  the  mountain  slopes.  This  is  especially  the  case  in  the 
Imerina  province  (in  which  the  capital,  Tananarive,  is  sit- 
uated), and  here  the  valley  soils  are  deep,  and  rich  in  humus. 
The  western  portion  is  but  thinly  forested.  The  soils  of  most 
of  the  island  are  "  red  "  with  ferric  hydrate,  resembling  the 
laterite  soils  elsewhere;  yet  the  iron  percentages  are  not  usually 
very  heavy,  ranging  mostly  from  4  to  6,  more  rarely  to  10% 
and  more,  of  ferric  oxid.  Most  of  the  red  soils  are  clayey, 
crack  open  in  summer  and  become  very  hard  in  drying. 

Of  the  476  soils  analyzed  by  Miintz  and  Rousseaux,  156  are 
from  the  province  of  Imerina,  56  from  the  adjacent  province 
of  Betsileo,  therefore  212  from  the  central,  mountainous  part 
of  the  island.  The  remainder  are  scattered  around  the  coasts; 
the  most  productive  being  apparently  those  of  the  northern 
end,  Diego  Suarez,  which  is  mostly  underlaid  by  the  eruptive 
rocks  forming  the  mountain  mass  of  Mount  Amber,  from 
which  numerous  fertile  valleys  radiate.  The  valleys  of  the 
we^t  coast  also,  in  the  provinces  of  Bara,  Tulear  and  Betsiriry, 
have  some  very  productive  soils. 

The  subjoined  table,  giving  fourteen  analyses  selected  as  rep- 
resentative from  the  mass  of  material  presented  by  Miintz  and 
Rousseaux,  gives  a  fair  general  idea  of  the  character  of  the 
soils  of  the  great  island.  It  is  at  once  apparent  that  lime  and 
potash  are  extremely  deficient  in  the  soils  of  the  mountain 
slopes  of  central  and  southern  Madagascar,  these  substances 
having,  as  elsewhere  in  the  humid  region,  been  leached  down 
into  the  valleys;  and  the  materials  being  mostly  quite  clayey, 
these  valley  soils  have  not,  as  in  the  case  of  the  sandy  alluvium 
of  the  Brahmaputra,  themselves  been  again  leached  of  their 
mineral  ingredients.  Practically  these  valleys  seem  to  form 
the  only  profitably  cultivable  area  of  the  central  portion;  while 
along  the  larger  river  courses,  such  as  the  Mangoky.  Ikopa, 
Mahajamba  and  others,  good  alluvial  "  bottoms  "  and  deltas 


408 


SOILS. 


< 

8 

b 
JH-S—    • 

< 

o" 

•Xsioq^s 

o    . 

X 

^ 

:       (ii.-g^" 

o 

^ 

to 

z 

o 

xe'ojs  «  « 

H 

< 

H 

_ 

•osojp 

8-8      ^S  ?  "S.""  •-  -o  '5  " 

n 
S 

<i 

o 

CO 

-UBiuuauij 

T!:        I?"    ^l.^S-3 

< 

"5.  5-5  ° 

H 

. 

u 

in 

o 

•EUEU 

X 

4)                ^              J£J  ^£ 

z 

w 

-lAoq-uBtu 

J* 

" 

q  2           *£  S1      X  2 

K 

>-3 

> 

U 

Q 

•EUEJ 

i|d 

-  rt-  J-a  6.  o   . 

Z 

<s 

0 

•XapuEiuo 
JEA  jo  -}sta 

IF 

*•*    r°  alj'lijil 

u 

3  J= 

M  „         »  «•«•«  i 

K 

H 

"* 

*9jquiytp 

"l-  *•* 

n  <J              *-•(>*       ^"ifi   O   «   5  *" 

< 

ro 

9U§ElUOTVr 

J^    r5 

^2             ^  "t        £*^<2^(ou 

a 
l/l 

< 
O 

o  " 

U  S0!  £1 

o 

U 

3     • 

w,    '    «  X 

a 

«-o          O1*     ACJ.—  *^.ti 

H 

^" 

ft 

'BIJJEUIBUy 

r-    ^" 

so  N          oo  «       u.2  !£"^r;3 

Q 

o" 

"  "•    ^  e  8  "  | 

z 

E 

il 

«5 

m 

—  '1 

o  J*            o  o       re  "^ 

S 

S 

03 

0 

z 

vO 

jo  q;nog 

•*  u              o-     **"  °"  o" 

o  2          o  o1      £  £  'S  «I 

p 

< 

<* 

i"   -^"IHA 

«|E-C 

z 

O 

x 

g  --»",.  S 

g 

S 

EuauiEosjuy 

•c—  •' 

%  a          jj     "S.2c  =  gS§] 

S"|8i:| 

h 

•XajiL'A 

»  J  2  >«  i) 

5 

U 

Xjoqo  8  u  o  j_ 

>o  o          «>n     £  °  £  °  '" 

u 
H 

^ 

«" 

jo  qiaou 

XjpUO>[Eg 
O     5[UEq      '^J 

oooo          oot^      re'"*^"" 

O-               OO        »-Cv.--—    „• 

'  -4-               '      o  «  g-o  J  5 

o 

I 

S 

0                                      X  ^    ^ 

N 

X3||EA    EAtp 

-*  u           \c*  S      "?  **  *** 

SJJ 

z 

£7" 

-UEJPUE  J 

o  2          n  o     J^  "^  x 

H 

o 

r      .a 

-*-»                  *      w  o  *^  aJ 

pa 

3 

c  *•;  r^ 

H 
Z 

f 

.^EZ 

-  g            ^   0^       H  3   2 

5 

-qiqoquiy 

q  2       q  q      —  o 

h 

*"*" 

*5   "^   cu 

z 

^  (J  *- 

< 

£3 

O 

3 

C  "   C    °>        .5rtCCT3 

z 

( 

vOO               Nt^        **  rt  '"^  S    x5  *^         ^  'c 

S 

j 

^ 

aqozE^uy 

Ji'S 

8~S          0*0     iB  "S."0  ^5  —  •=  So  c  o  ^ 

s 

i 

0 

oils  sSrS'S.fe 

z 

—,"    0 

H 

U 

£ 

•Xquioai 
-iqoquiy 

41  'o 

"     '    o-          '        C/2  "3    w 

•  "TiO-l 

'o 

X  O  "^ 

^ 

X 

d  v"%              , 

0 

J3 

C     '^'i  •<  '"'                "tS 

J) 

O 

tJd  ^""2  "^              E 

E 

hj 

¥  ,«  .2  "^  '§  c 

3 

_C  ^--  S  ^  "^    ?fl 

^ 

mill 

SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  409 

form  available  lands.  It  seems  to  the  writer  that,  in  view  of 
their  own  expressed  opinion  that  tropical  soils  are  not  to  be 
gauged  on  the  same  percentage-basis  of  soil-ingredients  as 
those  of  temperate  regions,  Miintz  and  Rousseaux  rather  un- 
derestimate the  productive  value  of  many  of  these  lands;  re- 
garding which  the  field  notes  report  good  production,  and 
the  crops  of  which  are  certainly  not  the  first  that  they  have 
borne  in  the  course  of  Malagassy  history.  It  is  as  though  their 
anxiety  to  forestall  overestimates  of  agricultural  prospects  by 
intending  settlers,  had  led  them  to  somewhat  overshoot  the 
mark. 

Be  that  as  it  may,  the  influence  of  the  tropical  climate  and 
rainfall  upon  the  composition  of  these  soils  is  certainly  very 
marked.  While  gneiss  is  not  credited  with  producing  first- 
class  soils,  its  usual  content  of  orthoclase  feldspar  should  at 
least  insure  a  respectable  average  content  of  potash ;  but  this, 
it  will  be  seen,  is  mostly  not  the  case;  and  that  of  lime  seems 
even  worse,  aside  from  the  case  where,  as  in  some  regions  near 
the  coast  (especially  in  the  west  and  south),  calcareous  forma- 
tions, probably  of  tertiary  age,  have  contributed  to  soil-for- 
mation. At  some  points  there  seem  to  exist  phosphate  deposits, 
well  known  elsewhere  to  occur  in  such  rocks,  which  impart  to 
the  soils  exceptionally  high  percentages  of  phosphoric  acid, 
even  exceeding  one  per  cent.  The  phosphates  of  course  remain 
practically  untouched  by  the  leaching  processes,  and  appear  to 
be  somewhat  widely  diffused ;  so  that  the  soils  of  Madagascar 
may  be  said  to  be,  on  the  whole,  well  supplied  with  this  import- 
ant plant-food. 

In  the  central  province  of  Tmerina  the  valleys  and  lower 
slopes  show  a  fair  content  of  both  lime  and  potash;  but  in  the 
province  of  Betsileo,  adjoining  it  on  the  south,  nearly  every 
one  of  the  soils  analyzed  is  reported  as  containing  only 
"traces"  of  lime,  together  with  very  small  amounts  of  potash 
in  most  cases.  The  ultimate  analyses  of  ignited  red  earths, 
of  which  an  average  is  here  given,  are  of  interest  in  this  con- 
nection. 

ULTIMATE  ANALYSIS   OF   IMERIXA  RED   SOILS,    IC.NITEO  ;   AVERAGE   OF  THREE. 

Silica 55.2 

Potash .3 

Lime trace 

Maijnesia i .  i 

P'erric  oxid 10.6 


410  SOILS. 

It  is  quite  obvious  that  only  leaching-down  and  concentration 
of  the  feeble  resources  of  such  material  in  the  valleys  can  pro- 
duce soils  worthy  of  permanent  cultivation. 

One  point,  however,  is  strikingly  illustrated  in  several  of 
the  analyses  given  in  the  subjoined  table.  We  find  in  the 
original  quite  a  number  of  cases  in  which  the  field  notes  report 
considerable  fertility,  while  the  chemists'  judgment  is  very 
unfavorable.  Thus  we  find  recorded  for  the  soil  No.  267, 
taken  near  the  village  of  Anjozorabe,  in  the  Maintirano  region, 
"  luxuriant  vegetation  and  remarkable  crops,"  with  such  mi- 
nute proportions  of  potash,  lime  and  phosphoric  acid  that  the 
authors  are  compelled  to  say  that  the  land  offers  "  no  cultural 
resources."  The  same  occurs  in  the  cases  of  soils  Nos.  370, 
261,  and  several  others  having  either  "  good  crops  "  or  "  abun- 
dant natural  vegetation."  Unless  we  assume  that  in  these 
cases  the  samples  were  not  properly  taken,  we  are  obliged  to 
conclude  that  under  the  local  climatic  conditions,  such  minute 
amounts  of  plant-food  are  developed  with  sufficient  rapidity  to 
supply  good  growth.  This  would  be  quite  parallel  to  the  case 
of  the  tea  soils  of  Assam,  whose  production  lasted  30  years 
before  showing  exhaustion,  on  plant-food  percentages  only 
slightly  greater  than  those  here  noted,  and  determined  by  a 
much  more  incisive  method. 

It  is  thus  quite  obvious  that  a  different  standard  of  inter- 
pretation must  be  applied  to  tropical  soils  as  compared  with 
either  the  temperate  humid,  or  the  arid  regions ;  and  that  uni- 
form methods  of  analysis  are  needed  to  evolve  a  definite  rule 
from  the  present  uncertainties. 

THE   SOILS    OF    INDIA. 

The  soils  of  India  have  been  investigated  to  some  extent  by 
the  geological  survey  of  India;  by  Voelcker,  who  went  there 
on  a  special  mission  to  investigate  agricultural  conditions; 
and  since,  more  especially  by  Leather,  Bamber  and  Mann ;  and 
by  Moreland.  Leather's  account  is  the  most  complete  on  the 
general  subject  and  can  best  serve  as  the  basis  for  a  review  of 
the  entire  peninsula.1 

According  to  Dr.  Leather,  "  the  four  main  types  of  soils  to 

*  On  the  Composition  of  Indian  Soils.     Agr.  Ledger,  1898,  No.  2. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  411 

be  dealt  with,  and  which  certainly  occupy  by  far  the  larger  of 
the  Indian  cultivated  area,"  are  :  The  Indo-Gangetic  alluvium, 
covering  the  chief  cultivable  areas  of  the  Indo-Gangetic  plain ; 
the  black  cotton  soils  or  regur,  occupying  the  main  body  of  the 
plateau  of  the  Central  provinces  (the  Deccan)  from  the 
Vindhya  range  south ;  the  red  soils  lying  on  the  metamorphic 
rocks  of  Madras;  and  the  "  latcrite"  soils  which  are  met  with 
in  many  parts  of  India.  To  these  should  be  added  the  alluvial 
soils  of  the  Brahmaputra  valley,  in  Assam.  It  is  hardly  to 
be  expected  that  so  large  an  area  as  that  of  India,  with  its 
diversified  topography,  and  a  climate  ranging  from  about  four 
inches  of  rainfall  in  the  northern  Pandjab  to  the  world's 
maximum  in  Assam,  and  southward  to  typical  tropical  condi- 
tions, could  be  even  thus  briefly  characterized.  The  observers 
have  rarely  given  for  the  several  soils  analyzed,  special  local 
and  climatic  data,  which  cannot  always  be  obtained  from  the 
official  publications;  so  that  it  is  not  easy  to  discuss  them  from 
the  points  of  view  of  aridity  and  humidity. 

The  Indo-Gangetic  Plain. — The  general  rain-map  of  India 
shows  the  Pandjab  and  Rajputana  to  be  arid  throughout; 
thence  eastward  the  rainfall  increases  to  25  and  30  inches  on 
the  Ganges;  notwithstanding  which,  alkali  (  reh  )  is  abundant 
about  Aligarh,  Meerut  and  Agra.  Thence  toward  Calcutta 
there  is  a  steady  increase  of  rainfall  until,  at  the  head  of  the 
Bay  of  Bengal,  70  inches  is  reached. 

If  under  these  conditions  the  Indo-Gangetic  plain  admits  of 
any  generalizations  as  regards  soil  composition,  it  must  be  at- 
tributed in  the  main  to  its  predominantly  alluvial  character. 
It  should  therefore  be  relatively  rich  in  lime,  magnesia  and 
potash.  So  far  as  the  first  is  concerned.  Leather  remarks  that 
the  only  rocky  particles  larger  than  sand  to  be  found  in  all 
this  large  belt  of  land  is  the  nodular  limestone  called  kankar, 
formed  by  the  deposition  of  calcium  carbonate  within  the  soil, 
at  the  depth  of  a  few  feet.  It  occurs  very  generally  in  India, 
and  as  stated  above  (chapters  9  and  19).  this  occurrence  of 
calcareous  hardpan,  of  varying  hardness,  is  almost  universal  in 
the  arid  regions.  The  analysis  given  in  the  table,  selected 
as  representative  from  those  given  by  Leather,  show  that 
the  general  forecast  is  realized  in  them,  as  soils  of  an  arid 
region. 


412 


SOILS. 


•    d 

?    *  Si  "  5  8"^"  8  »  S  "S- 

rs      « 

-OBSJE^      'EUJSI^J 

>O          *"                                   "        i    "    ' 

»       ' 

Ig 

g, 

•wa 

•2     -  5°S  S?^Nf.?;  «j  3>» 

S      * 

•          0 

•tpdouupuj. 

u,           „«     ^-^22     « 

§ 

•spos  8  1 

»      ^wS-Jr^-'^^o^ 

8M 
O 

£ 

oo                          t^  o       •  -  -o 

8 

< 

c 

81    oo'^So^So':-? 

Q           1A 

Q 
S5 

•c 

E  S 
.2  =« 

o- 

8       ' 

f 

d, 

J  « 

£    S^SS'^S;'^.::?? 

8     £ 

K 
H 

re 
•o 

« 

-             "     ^^     :    -° 

8     ' 

S 

H 

« 

• 

uniBquiEjE.r 

'     t^        O    «    •**•  t^*  —    r>.\c    O     •    **   M 

8     g 

S 

S 

11 

•Hodomtpux 

g                 •"«     : 

8     ' 

J°-« 

'IBS 

!J     «2^,S.:o^^o':2.o 

8    | 

tt 

-ipniQ  -EjnpBj^ 

a            ««    :   - 

8 

"I10S 

«     ?^gS2~8'oo«j:-oo' 

8     ? 

vO                      2                O  OO    2     *          M 

H        -    •-,  : 

1     ' 

s 

^    <:S,S,":5>&,-2<s;u-2c; 

c 

<: 
5 

^^^                    H  H 

o 

>> 

- 

x 

t/2 

"a 

•JOUJSIQ 

*8      «  °S  ^^5-o"  N°§  -^  5 

8     ? 

-S 

&, 
o 

•c 

c 

V 

uinqqqSmg 

S    ^          *-     j 

8     ' 

_>. 

N 
<% 

en 

^          0    *TX>    -    t~.  I-     .  0    - 

8     2 

M 

j 

o 

•efcpjnioq 

a*                           oo  oo        •       « 

8     ' 

en 

uiniAnnv 

N            -*-\O  O     0       .NOON           00 

•§ 

b, 
O 

3 

Epa^UBSBsdjS 

a- 

C/D 

3 

•uiniAnnv 

oo      XNN1o'S.:^2'SS       5, 

OC 

W 

C/5 

rt 

-SlNJ        'JEllSEIOf) 

^         i"" 

5* 

3 

3 

•tuniAnjiv  MSN; 

S     n  -  -  S  :CE.<S"S  S     " 

o 

<J 

•andiuu^E-! 

«?                :  N>0         ^ 

d 

< 

C 

•uiniAnnv  p[Q 

"     S  2>  o^-  -°c  o"S"o     S 

r 

S 

•5(UEq  jndzaj 

00                                     •                                   "" 

>, 

J3 

to 

'S[1OS 

OC             •    N    -    f  O-OO    C-  t^  C  00    r-. 

w%       -  oo  c  o  •"•  i^iao  o  o  N  c- 

8     =, 

S 

--. 

< 

5 

X 

I 

I 

-[£3  'jndqic; 

R       J^-^KKi 

8 

< 

*•" 

u 

•SUIEO'J 

'c     o"S'£3>:2'%c§£>£3- 

8     C 

X 

K 
H 

O 

'saSiiEf)    'uosj 

00 

8      ' 

X 

bfl 

•S|1OS  XlUEO'I 

?.    3;  N1^  K.  -  -  "2)  -  S  S^ 

8    -5 

S 

0 

rt 

O 

.5, 

•BSUEJV  E3UE.,3 

oo 

8 

X 

-c 

C 

S-,UBO-I  A*p 

^    ^=8  ?  S  :  S.51  ^.  ?i- 

8     8 

X3UBA  «}0S 

00                            "     '•    * 

8 

•  :  •  :  •  -^  

::::::  C^    3  :  |  j 

^  ^  i  J.  :  51  ="  -  ~~;z  '^^  MI 
^3'§~'"^c  j'S'-i'f-'i  =  S 

"3 

1 
£ 

SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 

The  Brahmaputra  Alluvium  in  Assam. — Aside  from  the 
immediate  alluvium  of  the  Indus,  of  which  no  definite  data  are 
available,  the  Indo-Gangetic  plain  represents  the  drainage  of 
the  southern  slope  of  the  Himalaya  chain.  That  of  most  of 
the  northern  slope  is  represented  by  the  Brahmaputra,  which 
not  only  orginates  in  a  region  of  heavy  precipitation — Thibet — 
but  continues  in  the  same  throughout  its  course,  and  rounding 
the  easternmost  spur  of  the  Himalaya  range  enters,  in  southern 
Assam,  upon  the  region  of  the  maximum  rainfall  known.  Its 
alluvial  deposits  should  therefore  show  the  reverse  character- 
istics of  those  of  the  Ganges ;  they  should,  as  thoroughly 
leached  soils,  be  poor  in  lime,  magnesia  and  potash.  We  have 
fortunately  on  this  subject  the  excellent  work  done  by  Mr. 
H.  H.  Mann  for  the  Indian  Tea  Association,  the  report  of 
which  was  published  in  1901,  and  contains,  besides  a  large 
number  of  analyses,  good  descriptions  of  the  general  soil  and 
cultural  conditions  of  the  Assam  tea  districts,  with  suggestions 
for  their  improvement. 

The  tea  plantations  of  Assam  are  located  almost  wholly  on 
the  new  and  old  alluvium  of  the  Brahmaputra  river,  bordered 
on  the  north  by  the  eastern  spur  of  the  Himalayas,  on  the 
south  by  the  low  ranges  of  the  Khasia  hills.  The  soil  is  mostly 
quite  sandy,  the  late  alluvium  gray  in  color,  the  older  reddish 
and  more  loamy.  Of  the  four  analyses  given  in  the-table  and 
fairly  representing  the  average  character  of  these  soils,  the  two 
first  are  from  the  north  side,  the  latter  two  from  the  south  side 
of  the  river. 

It  will  be  noted  that  the  prominent  feature  of  all  these  soils 
is  an  extremely  low  percentage  of  lime,  the  general  average 
being  about  .o8r/<  as  against  nearly  i.orv  in  the  average 
Indo-Gangetic  soils.  In  the  latter,  potash  ranges  between  .6^ 
and  .~or/f  ;  in  the  Assam  soils  between  .25  and  .35.  Magnesia 
averages  nearly  1.3  in  the  Indo-Gangetic.  against  about  .50  in 
the  Assam  tea  soils.  It  is  thus  apparent  that  the  same  general 
facts  as  regards  the  leaching-out  of  soil  ingredients  already 
shown  for  eastern  and  western  Xorth  America  are  strikingly 
verified  in  northern  India:  but  reversed  as  regards  the  points 
of  the  compass.  The  preferential  leaching-out  of  lime  as  com- 
pared with  magnesia  and  potash,  is  here  again  well  exemplified. 
It  would  be  interesting  to  have  an  analysis  of  the  Brahma- 


414 


SOILS. 


putra  water  to  compare  with  that  of  the  Ganges.  That  tea 
should  flourish  for  twenty  to  thirty  years  in  such  soils,  is  a 
good  indication  of  one  cause  at  least  of  the  total  failure  of  tea 
culture  in  California,  where  tea  plants  are  difficult  to  maintain 
alive,  and  after  25  years  form  rounded,  scrubby  bushes  not 
over  four  feet  high.  Similar  failures  of  tea  on  calcareous  soils 
are  on  record  from  India.  The  low  lime-content  of  the  Assam 
soils,  then,  does  not  necessarily  imply  that  these  soils  should 
be  limed  to  maintain  tea  production.  According  to  Mann, 
the  main  deficiency  is  in  nitrogen,  as  the  figures  imply;  but 
whether  his  recommendation  of  green-manuring  with  legu- 
minous crops  to  increase  the  nitrogen-supply  is  practicable 
without  first  supplying  more  lime  to  the  Assam  soils,  is  ques- 
tionable. Since  phosphoric  acid  is  also  low,  his  recommenda- 
tion to  use  freely  the  basic  or  Thomas  slag  is  doubtless  a  good 
one,  since  lime  would  thus  also  be  moderately  increased. 

Bamber  gives  a  number  of  analyses  of  tea  soils  from  low 
ground  in  Assam,  which  are  very  rich  in  vegetable  matter  and 
quite  acid.  Like  those  reported  by  Leather,  these  "  bhil  "  soils 
are  very  poor  in  lime  and  nitrogen,  but  fairly  supplied  with 
potash  and  phosphoric  acid. 

The  Regur  or  Black  Cotton  Soils  of  Southern  India. — The 
second-greatest  reasonably  uniform  soil-area  of  India  is  that 
covered  by  the  regur,  or  black  cotton  soils,  in  south  central 
India,  notably  the  Deccan.  where  these  soils  are  said  to  have 
been  cultivated  without  fertilization  for  2000  years  and  are  still 
fairly  productive.1  Both  in  their  physical  character,  chemical 
composition,  and  cultural  characteristics,  these  regur  soils 
are  very  similar  to  the  "  prairie  soils  "  of  the  Cotton  states 
and  especially  to  the  "  black  adobe  "  of  California.  Like  the 
latter  they  are  of  unusual  depth  without  change  of  tint ;  they 
crack  wide  open  during  the  dry  season  on  account  of  their  high 
clay  content;  and  the  soil  is  thus  partly  inverted  by  the  surface 
soil  falling  into  the  cracks.  To  the  latter  fact  Leather  as- 

1  That  is  to  say,  they  now  produce  about  600  pounds,  or  10  bushels  of  wheat 
per  acre,  as  do  the  Rothamstead  soils  after  fifty  years'  exhaustive  cultivation. 
Probably  both  have  come  down  to  the  permanent  level  of  production  correspond 
ing  to  the  amount  of  plant-food  made  currently  available  each  year  by  the  fallow- 
ing process  in  originally  very  rich  soils.  The  present  product  of  cotton  on  the 
regur  lands  does  not  seem  to  be  on  record;  judging  by  the  wheat  product  it 
should  not  be  over  one  hundred  pounds  of  lint  per  acre. 


SOILS  OF  THE  ARID   AND  HUMID  REGIONS.  415 

cribes,  in  part,  the  long  duration  of  fertility  in  the  regur  lands. 
The  regur  also  contains  fragments  of  calcareous  hardpan  (here 
called  guvarayi),  just  as  in  the  Great  Valley  of  California. 
The  eighteen  analyses  of  regur  given  by  Leather  agree  so 
nearly  in  their  essential  points  that  it  is  admissible  to  average 
them ;  two  other  examples  are  however  also  given  in  the  table. 

It  will  be  noted  that  while  the  contents  of  lime,  magnesia  and 
alumina  are  uniformly  high,  the  content  of  potash  has  a  wide 
range;  it  rises  very  high  (i.i4</fc)  in  the  maximum,  while  the 
average  is  fair. 

One  conspicuous  defect  of  these  soils  is  their  extremely  low 
content  of  nitrogen,  in  view  of  which  their  lasting  productive- 
ness is  difficult  to  understand ;  unless  it  be  that,  as  in  California, 
their  high  lime-content  causes  a  copious  crop  of  leguminous 
weeds,  constantly  replacing  the  nitrogen  supply.1  Unfor- 
tunately we  have  no  determinations  of  humus  or  of  its  nitrogen- 
content.  Leather  attributes  the  black  color  of  the  regur  to 
some  mineral  substance  rather  than  to  humus;  but  his  argu- 
ments are  not  quite  convincing,  so  long  as  the  firandean  test 
has  not  been  made.  In  view  of  the  low  rainfall  and  the  close- 
ness of  the  texture  of  regur,  it  is  probable  that  little  if  any 
nitrates  are  currently  washed  out  of  the  black  cotton  lands. 

The  regur  soil-sheet  seems  to  be  underlaid  over  the  greater 
part  of  its  area  by  a  basaltic  eruptive  sheet  ( not  by  meta- 
morphic  rocks,  as  stated  by  Leather),  and  it  is  not  easy  to  con- 
ceive how  such  a  soil  stratum  can  have  been  formed  from  such 
rocks  as  a  sedentary  formation.  Elsewhere  such  soils  are 
usually  rather  light  and  porous,  as  is  the  case  in  the  Hawaiian 
and  Samoan  islands;  and  very  high  in  iron-content.  The 
regur  has  the  character  of  an  alluvial  backwater  or  lake  de- 
posit; but  how  such  a  formation  can  have  occurred  on  the 
Deccan  plateau,  is  a  question  not  easily  answered. 

Red  Soils  of  the  M  minis  Region. — Interspersed  with  and  to 
seaward  of  the  regur  lands  there  are  in  the  Madras  presidency 
considerable  bodies  of  "  red  "  lands,  which  appear  to  be 
sedentary  soils  formed  from  underlying  dark-colored,  mostly 
eruptive  rocks.  Some  of  these  are  very  rich  in  lime  and  pot- 
ash, others  very  poor,  and  it  seems  impossible  to  classify  them 

1  See  Voelcker,  Report  on  the  Improvement  of  Indian  Agriculture,  1892,  p.  46^ 
par.  60. 


416  SOILS. 

under  any  definite  category  either  from  the  chemical  or  physical 
point  of  view,  except  as  to  their  red  tint.  Even  this  tint,  how- 
ever, is  not  always  found  associated  with  exceptionally  high 
contents  of  iron  oxid,  but  due  rather  to  its  fine  diffusion  in  the 
soil  mass.  As  compared  with  the  regur,  with  which  the 
"  red  "  areas  are  interspersed,  these  soils  contain,  on  the  aver- 
age, less  lime,  potash  and  ferric  oxid;  and  phosphoric  acid  is 
uniformly  low.  The  alluvial  (brown  and  black)  soils  from 
the  same  region,  exemplified  in  the  table,  are  doubtless  derived 
partly  from  the  regur,  and  their  color  and  composition  varies 
accordingly. 

"  Laterite  Soils." — These  are  defined  by  Wohltmann  ( Trop- 
ische  Agricultur,  1892)  as  being  "  the  characteristic  sedentary 
soils  (Verwitterungsboden)  of  the  tropics,  formed  under  the 
influence  of  heavy  precipitation,  high  temperatures  and 
drought."  This  definition  does  not  indicate  their  derivation 
from  any  particular  rock,  such  as  laterite  is  supposed  to  be ;  but 
its  definition  puzzles  even  geologists,  and  so,  as  Leather  ob- 
serves, the  definition  of  laterite  soils  will  naturally  puzzle 
agricultural  chemists.  Accordingly  it  is  difficult  to  deduce 
from  the  analyses  given  any  definite  common  characters. 
Leather  describes  those  analyzed  by  him  as  red  or  reddish, 
sandy  and  gravelly,  the  gravel  or  cobbles  often  incrusted  with 
a  dark-smooth  crust  of  limonite,  which  to  the  uninitiated  looks 
as  though  the  rock  itself  had  been  fused  and  vitrified.  The 
samples  from  Lohardaga  and  Singhbhum  show  the  effects  of 
these  limonite  crusts  upon  the  composition  of  the  soils,  which 
resembles  that  of  the  Hawaiian  soils  mentioned  above ;  but  in 
the  latter  the  iron  oxid  is  wholly  pulverulent.  But  it  is  prob- 
able that,  as  in  the  case  of  the  latter,  the  high  content  of 
phosphoric  acid  shown  in  the  statement  ( .64  for  the  Lohardaga 
soil)  is  tightly  locked  up  in  the  insoluble  form  of  ferric  phos- 
phate. Wohltmann's  definition  of  laterite  soils  seems  best  rep- 
resented by  the  "  terra  roxa  "  of  Brazil,  which  as  he  states  has 
.02  to  .08%  of  potash.  .02  to  .10%  of  lime,  and  .045  to 
.10%  of  phosphoric  acid.  Humus  and  nitrogen  are  very  de- 
ficient in  all  these  soils. 

While  most  prominent  in  the  coast  region  of  Bengal,  they 
also  occur  not  only  near  Madras  (Saidapet)  but  also  in  the 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS.  417 

belt  of  high  rainfall  on  the  Malabar  (western)  coast  of  the 
Indian  peninsula.  ' 

The  productiveness  of  the  laterite  soils  seems  throughout  to 
be  only  moderate,  yet  much  higher  than  would  be  expected  of 
soils  of  similar  composition  in  the  temperate  zones,  where  the 
rate  of  soil-formation  is  so  much  slower  than  in  the  tropics. 

From  the  analyses  of  "  coffee  soils  "  from  Yarcand  in  the 
Sheveroy  hills,  north  of  Madras,  we  learn  that  coffee  does  well 
with  a  fairly  liberal  supply  of  lime  (.30  to  .44%}  and  phos- 
phoric acid,  but  is  satisfied  with  a  much  smaller  amount  of 
potash  than  is  found  in  the  tea  soils  of  Assam. 

A  farther  systematic  investigation  of  the  soils  of  India,  with 
simultaneous  accurate  observations  on  their  depth,  subsoil, 
geological  derivation,  topographical  location  and  relations  to 
rainfall,  could  not  fail  to  yield  very  important  practical  results. 
The  examination  of  samples  collected  and  sent  in  by  persons 
unfamiliar  with  the  proper  mode  of  taking  soil  specimens,  and 
the  information  which  should  accompany  them,  always  in- 
volves a  great  deal  of  uncertainty  and  waste  of  labor,  and  in- 
clefiniteness  of  results. 

INFLUENCE   OF   ARIDITY   UPON    CIVILIZATION. 

In  connection  with  the  facts  given  and  discussed  above,  as 
to  the  relative  productive  capacity  of  lands  of  the  humid  and 
arid  regions,  it  becomes  of  interest  to  consider  what  influence, 
if  any,  these  differences  may  have  had  in  determining  the 
choice  of  the  majority  of  the  ancient  civilizations  in  favor  of 
countries  where  nature  imposes  upon  the  husbandman,  who 
supplies  the  prime  necessaries  of  life,  the  onerous  condition  of 
artificial  irrigation.1 

Preference  of  .-Indent  Civilizations  for  Arid  Countries. — A 
brief  review  suffices  to  establish  the  fact  of  such  choice.  Aside 
from  Egypt,  the  permanent  fertility  of  which  is  ascribed  to  the 
inundations  of  the  Nile,  we  find  to  westward  the  oases  of  the 
Libyan  and  Sahara  deserts,  the  high  fertility  of  which  has 
become  proverbial  and  has  caused  them  to  be  cultivated  from 
ancient  times  to  the  present.  Similarly,  on  both  sides  of  the 

1  Verhandlungen  tier  Deutschen  Physiologischen  desellschaft  in  Berlin,  Decem. 
ber    1892;  North  American  Review,  September,  190^. 


4i8  SOILS. 

Mediterranean  Sea,  we  find  that,  instead  of  the  humid  forest 
country,  it  was  in  the  arid  but  irrigable  coast  countries,  such  as 
the  vegas  of  Valencia,  Alicante,  Granada,  Malaga,  and  the 
even  more  arid  domain  of  which  Carthage  was  the  metropolis ; 
and  farther  east,  in  the  Graeco-Syrian  archipelago  and  the  ad- 
jacent coasts,  that  noted  centers  of  civilization  were  developed 
and  maintained.  Thence  the  arid  belt  requiring  irrigation 
extends  from  Egypt  and  Arabia  to  Palestine,  Syria,  Assyria, 
Mesopotamia  and  Persia,  and  across  the  Indus  through  the 
anciently  recognized  regions  of  Indian  civilization — Sindh, 
the  Panjab,  Rajputana  and  the  Northwestern  provinces — to 
the  Ganges,  embracing  such  well-known  centers  as  Lahore, 
Delhi,  Meerut,  Agra,  etc.,  inhabited  by  much  more  hardy  and 
progressive  races  than  the  humid  and  highly  productive  tropical 
portions  of  the  Indian  peninsula.  Throughout  the  extensive 
and  important  portion  of  northern  India,  irrigation  is  neces- 
sary to  maintain  regular  production;  and  in  default  of  it, 
periodic  famines  ravage  the  country.  Thousands  of  years  ago, 
millions  upon  millions  of  treasure  were  expended  there  upon 
irrigation  works,  as  has  again  been  done  in  modern  times;  yet 
in  the  rainy,  forested  districts  we  still  find  large  areas  prac- 
tically tenanted  by  wild  beasts.  In  Asia  Minor,  as  well  as  in 
Central  Asia,  the  remains  of  ancient  cities  once  surrounded  by 
richly  productive  irrigated  fields,  are  found  where  at  present 
only  the  herds  of  nomads  pasture.  The  Khanates  of  southern 
Turkestan  with  their  historic  cities,  illustrate  the  same  obsti- 
nate bias  in  favor  of  arid  climates.  Similarly,  in  the  New 
World,  it  was  not  in  the  moist  and  exuberantly  fertile  forest 
lands  of  the  Orinoco  and  Amazon,  but  on  the  arid  western 
slopes  of  the  Andes,  that  the  civilization  of  the  Incas  was  de- 
veloped. In  Mexico,  also,  it  was  the  high  central,  arid  plateau, 
not  the  bountifully  productive  ticrra  calicnte,  over  which  the 
Aztecs  chose  to  establish  the  main  centers  of  their  empire. 
Even  to  northward,  the  inhabitants  of  the  high,  dry  plains  of 
Arizona  and  New  Mexico  were,  as  their  descendants  of  the 
Pueblos  are  to-day,  superior  in  social  development  to  their 
forest-dwelling  neighbors  of  the  Algonquin  race.  From  time 
immemorial  they  have  practiced  irrigation  in  connection  with 
cultivation,  maintaining  a  comparatively  dense  population  on 
very  limited  areas. 


SOILS  OF  THE  ARID  AND  HUMID  REGIONS. 


419 


It  might  be  thought  that  the  desire  to  avoid  the  labor  of 
clearing  the  forest  ground  was  the  motive  which  guided  the 
choice  of  the  ancient  nations  toward  the  cheerless-looking,  tree- 
less regions. 

But  if  we  consider  the  cost  and  labor  of  establishing  and 
maintaining  irrigation  ditches,  it  certainly  seems  that  a 
stronger  motive,  based  on  the  intrinsic  nature  of  the  case,  must 
have  influenced  their  selection.  Neither  can  we  with  any 
degree  of  plausibility  ascribe  the  preference  for  the  arid  open 
country  to  the  fear  of  enemies  lurking  in  the  forest,  since  war 
was  in  early  times  practically  the  normal  condition  of  man- 
kind, and  was  waged  with  little  hesitation  wherever  booty  was 
in  sight.  It  has  also  been  asked  how  the  ancients  could  have 
known  of  the  high  productive  capacity  of  arid  lands ;  but  no 
one  who  has  ever  seen  the  springing-up  of  luxuriant  vegeta- 
tion after  the  periodic  overflows  of  the  arid-region  streams,  or 
the  same  surrounding  the  springs  in  the  deserts,  would  ask  that 
question. 

Irrigation  necessitates  Co-operation. — Irrigation  enterprises 
can  be  accomplished  in  a  very  limited  degree  only  by  individ- 
uals or  even  families.  Its  permanently  successful  execution  re- 
quires the  co-operation  of  at  least  several  social  groups,  ulti- 
mately of  communities  and  states,  if  it  is  not  to  give  rise  to 
acrimonious  contentions  or  actual  warfare;  witness  the  "  shot- 
gun policy  "  resorted  to  in  the  arid  \Yest  in  times  not  very 
remote.  Irrigation,  in  other  words,  compels  co-operative  social 
orgari/.alion  quite  different  from  and  far  in  advance  of  that  neces- 
sary in  humid  countries.  And  such  organization  is  mani 
festly  conducive  to  the  preservation  and  development  of  the 
arts  of  peace,  which  means  civilization.  The  most  ancient 
systematic  code  of  laws  known  to  us  is  that  of  Hammurabi,  the 
king  of  arid  .Assyria. 

The  higli  ami  permanent  produetireness  of  arid  soils  induces 
pcnnanenee  of  ck'il  organization. — In  humid  countries,  as  is 
well  known,  cultivation  can  only  in  exceptional  cases  be  con- 
tinued profitably  for  many  years  without  fertilization.  But 
fertilization  requires  a  somewhat  protracted  development  of 
agriculture  to  be  rationally  and  successfully  applied  in  the 
humid  regions,  and  the  Germanic  tribes,  like  the  North-Ameri- 
can Indians,  seem  to  have  shifted  their  culture  grounds  fre- 


420 


SOILS. 


quently  in  their  migrations.  No  such  need  was  felt  by  the 
inhabitants  of  the  arid  regions  for  centuries,  for  the  native 
fertility  of  their  soils,  coupled  with  the  fertilizing  effects  of 
irrigation  water  bringing  plant-food  from  afar,  relieved  them 
of  the  need  of  continuous  fertilization ;  while  in  the  humid 
regions,  the  fertility  of  the  land  is  currently  carried  into  the  sea 
by  the  drainage  waters,  through  the  streams  and  rivers,  causing 
a  chronic  depletion  which  has  to  be  made  up  for  by  artificial 
and  costly  means.  What  with  the  greater  intrinsic  fertility 
and  the  great  depth  of  soil  available  for  plant  growth,  much 
smaller  units  of  land  will  suffice  for  the  maintenance  of  a 
family  in  arid  countries ;  a  fact  which  is  even  now  being  il- 
lustrated in  the  irrigated  region  of  the  United  States,  where 
ten  acres  of  irrigated  land  instead  of  40  or  160,  as  in  the  East, 
form  the  unit. 

The  arid  regions  were,  therefore,  specially  conducive  to 
the  establishment  of  the  highly  complex  polities  and  high 
culture,  of  which  the  vestiges  are  now  being  unearthed  in  what 
we  are  in  the  habit  of  calling  "deserts;"  the  very  sands  of 
which  usually  need  only  the  lifegiving  effects  of  water  to 
transform  them  into  fruitful  fields  and  gardens.  It  is  also 
quite  natural  that  the  wealthy  and  prosperous  communities 
so  formed  should  in  the  course  of  time  have  excited  the 
cupidity  of  the  "  barbarous  "  forest-inhabiting  races,  and  as 
history  records,  have  been  over  and  again  overwhelmed  by 
them — a  similar  fate  often  afterwards  overtaking  the  con- 
querors in  their  turn,  after  the  Capuan  ease  of  their  existence 
had  weakened  their  warlike  prowess.  At  the  present  time, 
the  arid  regions  of  the  old  world  are  still  largely  suffering  from 
having  been  overrun  by  the  nomadic  Turanians,  whose 
original  habitat — Mongolia  and  Turkestan — while  also  arid, 
does  not  permit  of  the  ready  realization  of  the  advantages 
above  outlined,  on  account  of  the  rigorous  climate  brought 
about  by  altitude.  Mahometanism  first  expelled,  and  has 
since  repelled,  occidental  civilization  from  the  arid  regions  of 
the  Old  World,  remaining  to-day  as'  an  obstacle  to  its  prog- 
ress. The  peaceful  aggression  of  railroads  and  telegraphs 
now  seems  likely  to  gradually  overcome  this  repulsion ;  and 
when  Constantinople  and  Bagdad  shall  be  linked  together  by 
the  steel  bands,  the  desert  will  lose  its  terrors,  and  Mesopotamia 


SOILS  OF  THE  ARID  AND  HUMID    REGIONS.  421 

and  Babylonia  will  again  become  garden  lands,  as  of  old, 
under  the  abundant  waters  of  the  Euphrates  and  Tigris. 
Until  the  water-supplies  of  the  arid  countries  shall  have  been 
more  definitely  gauged,  it  is  impossible  to  foretell  to  what  ex- 
tent food-production  may  be  increased  by  their  cultivation 
under  irrigation,  after  the  relief  from  political  misrule  shall 
have  rendered  such  undertakings  safe.  But  it  can  even  now  be 
foreseen  that  with  improved  modern  methods  of  cultivation, 
the  productive  area  of  the  world  can  be  vastly  increased  by  the 
utilization  of  the  countries  where,  as  the  Turcomans  say,  "  the 
salt  is  the  life  of  the  land." 


CHAPTER  XXII. 

ALKALI  SOILS. 

Alkali  Lands  and  Sea-shore  Lands. — Alkali  lands  proper,  as 
already  stated,  are  wholly  distinct  in  their  nature  and  origin 
from  the  salty  lands  of  sea-coast  marshes,  past  or  present. 
The  latter  derive  their  salts  from  sea-water  that  occasionally 
overflows  them,  or  from  that  which  has  evaporated  in  segre- 
gated basins  or  estuaries ;  and  the  salts  impregnating  them  are 
essentially  "  sea  salts,"  that  is,  common  salt,  together  with 
bittern  (magnesium  chlorid),  Epsom  salt  (magnesium  sulfate) 
gypsum,  etc.  (see  chapter  2,  p.  26).  Very  little  of  what  would 
be  useful  to  vegetation  or  desirable  as  a  fertilizer  is  contained 
in  the  salts  impregnating  such  soils ;  and  they  are  by  no  means 
always  intrinsically  rich  in  plant-food,  but  vary  greatly  in  this 
respect. 

While  sea-shore  lands  are  by  no  means  always  of  high  fer- 
tility even  when  freed  from  their  salts,  especially  when  very 
sandy,  it  is  otherwise  when  they  occur  near  the  mouths  of 
streams  or  rivers,  whose  finest  sediments  they  then  receive. 
From  such  lands  are  formed  the  profusely  productive  Polders 
of  Holland  and  northern  Germany,  and  the  equally  noted 
"  colmates  "  of  France  and  Italy.  These,  so  soon  as  freed 
from  salt,  may  be  considered  as  possessing  the  same  advantages 
as  "  delta  "  alluvial  lands,  and  from  the  same  causes ;  notably 
the  accumulation  of  the  finest  sediments  derived  from  the 
rivers'  drainage  basins. 

Origin. — Alkali  lands  proper  bear  no  definite  relation  to  the 
present  sea ;  they  are  mostly  remote  from  it  or  from  any  other 
sea  bed,  so  that  they  have  sometimes  been  designated  as 
"  terrestrial  salt  lands."  Their  existence  is  in  the  majority  of 
cases  definitely  traceable  to  climatic  conditions  alone.  They 
are  the  natural  result  of  a  light  rainfall,  insufficient  to  leach 
out  of  the  land  the  salts  that  always  form  in  it  by  progressive 
weathering  of  the  rock  powder  of  which  all  soils  largely  con- 

422 


ALKALI  SOILS. 


423 


sist.  Where  the  rainfall  is  abundant,  that  portion  of  the  salts 
corresponding  to  "  sea  salts  "  is  leached  out  into  the  bottom 
water,  and  with  this  passes  through  springs  and  rivulets  into 
the  country  drainage,  to  be  finally  carried  to  the  ocean.1  An- 
other portion  of  the  salts  formed  by  weathering,  however,  is 
partially  or  wholly  retained  by  the  soil;  it  is  that  portion  chiefly 
useful  as  plant  food. 

It  follows  that  when,  in  consequence  of  insufficient  rainfall, 
all  or  most  of  the  salts  are  retained  in  the  soil,  they  will  contain 
not  only  the  ingredients  of  sea-water,  but  also  those  useful  to 
plants.  In  rainy  climates  a  large  portion  even  of  the  latter 
is  leached  out  and  carried  away.  In  extremely  arid  climates, 
on  the  contrary,  the  entire  mass  of  the  salts  remains  in  the 
soils;  and,  being  largely  soluble  in  water,  evaporation  during 
the  dry  season  brings  them  to  the  surface,  where  they  may 
accumulate  to  such  an  extent  as  to  render  ordinary  useful 
vegetation  impossible;  as  is  seen  in  "alkali  spots,"  and  some- 
times in  extensive  tracts  of  '  alkali  desert.''  Three  compounds, 
viz.  the  sulfate.  chlorid  and  carbonate  of  sodium,  usually  form 
the  main  mass  of  these  saline  efflorescences.  Magnesium  sul- 
fate (Epsom  salt)  is  in  many  cases  a  very  abundant  ingredient; 
some  calcium  sulfate  is  nearly  always  present,  and  calcium 
chlorid  is  not  infrequently  found. 

In  some  cases  the  above  salts  are  in  part  at  least  derived  from  the 
leaching  of  adjacent  or  subjacent  geological  deposits  impregnated  with 
them  at  the  time  of  their  formation.  Such  is  the  case  in  portions  of 
Wyoming,  Colorado  and  New  Mexico,  in  the  Colorado  river  delta,  and 
in  the  Hungarian  IMain  ;  and  it  is  in  these  cases  especially  that  the 
chlorids  of  calcium  and  magnesium  also  form  part  of  the  saline  mixture. 

Geographical  Distribution  of  Alkali  Lands. — In  looking  over 
a  rainfall  map  of  the  globe'2  we  see  that  a  very  considerable 
portion  of  the  earth's  surface,  forming  two  belts  to  poleward 
of  the  two  tropics,  has  deficient  rainfall;  the  latter  term  being 
commonly  meant  to  imply  any  animal  average  loss  than  jn 
inches  (500  millimeters).  The  arid  region  thus  defined  in- 
cludes, in  North  America,  most  of  the  country  lying  west  of 
the  one  hundredth  meridian  up  to  the  Cascade  Mountains,  and 

1  See  Chapter  2,  p.   26.  J  See  above,  chapter  16,  p.  294. 


424 


SOILS. 


northward  beyond  the  line  of  the  United  States ;  southward,  it 
reaches  far  into  Mexico,  including  especially  the  Mexican 
plateau.  In  South  America  it  includes  most  of  the  Pacific 
Slope  (Peru  and  Chile)  south  to  Araucania;  and  eastward  of 
the  Andes,  the  greater  portion  of  the  plains  of  western  Brazil 
and  Argentina.  In  Europe  only  a  small  portion  of  the 
Mediterranean  border  is  included;  but  the  entire  African  coast- 
belt  opposite,  with  the  Saharan  and  Libyan  deserts,  Egypt  and 
Arabia,  are  included  therein,  as  well  as,  south  of  the  Equator,  a 
considerable  portion  of  South  Africa  (Kalahari  desert).  In 
Asia,  Asia  Minor,  Syria  (with  Palestine),  Mesopotamia, 
Persia,  and  northwestern  India  up  to  the  Ganges,  and  north- 
ward, the  great  plains  or  steppes  of  central  Asia  eastward  to 
Mongolia  and  western  China,  fall  into  the  same  category;  as 
does  also  a  large  portion  of  the  Australian  continent. 

Utilisation  of  World-wide  Importance. — Over  these  vast 
areas  alkali  lands  occur  to  a  greater  or  less  extent,  the  excep- 
tions being  the  mountain  regions  and  adjacent  lands  on  the  side 
exposed  to  the  prevailing  winds.  It  will  therefore  be  seen 
that  the  problem  of  the  utilization  of  alkali  lands  for  agricul- 
ture is  not  of  local  interest  only,  but  is  of  world-wide  import- 
ance. It  will  also  be  noted  that  many  of  the  countries  referred 
to  are  those  in  which  the  most  ancient  civilizations  have  ex- 
isted in  the  past,  but  which  at  present,  with  few  exceptions,  are 
occupied  by  semicivilizecl  people  only.  It  is  doubtless  from 
this  cause  that  the  nature  of  alkali  lands  has  until  lately  been 
so  little  understood,  that  even  their  essential  distinctness  from 
the  sea-border  lands  has  been  but  recently  recognized  in  full. 
Moreover,  the  great  intrinsic  fertility  of  these  lands  when 
freed  from  the  noxious  salts,  has  been  very  little  appreciated ; 
their  repellent  aspect  causing  them  to  be  generally  considered 
as  permanently  waste  lands. 

Repellent  aspect. — This  aspect  is  essentially  due  to  their  natural 
vegetation  being  in  most  cases  confined  to  plants  useless  to  man,  com- 
monly designated  as  "saline  vegetation,"  J  of  which  but  little  is  usually 
relished  by  cattle.  Notable  exceptions  to  this  rule  occur  in  North  and 
South  America,  Australia,  and  Africa,  where  the  "  saltbushes  "  of  the 
former  and  the  "  karroo  "  vegetation  of  the  latter  form  valuable  pasture 

1  See  Chapter  23. 


ALKALI  SOILS. 


425 


426  SOILS. 

and  browsing  grounds.  Apart  from  these,  however,  all  efforts  to  find 
culture  plants  for  these  lands  generally  acceptable,  or  at  least  profitable, 
in  their  natural  condition,  have  not  been  very  successful. 

Figure  60  illustrates  the  usual  aspect  of  alkali  lands  in  the  San 
Joaquin  valley  of  California.  It  will  be  noted  that  the  alkali-covered 
surface  is  only  in  spots,  with  clumps  of  vegetation  between,  so  that 
cattle  can  find  both  pasture  and  browsing  on  a  portion  of  such  lands, 
even  though  the  plants  so  growing  are  not  usually  of  the  most  desirable 
kind.  We  find  in  all  arid  regions,  however,  considerable  areas  either 
wholly  destitute  of  vegetation,  or  bearing  only  such  saline  growth  as  is 
rejected  by  all  kinds  of  domestic  animals. 

Effects  of  Alkali  upon  culture  plants. — In  land  very  strongly 
impregnated  with  alkali  salts,  most  culture  plants,  if  their  seed 
germinates  at  all,  will  show  a  sickly  growth  for  a  short  time, 
"  spindle  up "  and  then  die  without  fruiting.  In  soils  less 
heavily  charged  the  plants  may  simply  become  dwarfed,  and 
fruit  scantily.  The  effect  on  grown  trees  around  which  alkali 
has  come  up,  is  first,  scanty  leafage  and  short  growth  of  shoots, 
themselves  but  sparsely  clothed  with  leaves.  This  state  of 
things  is  well  shown  in  figures  61  and  62,  which  represent 
apricot  trees  growing  but  a  short  distance  apart,  but  one  com- 
ing within  range  of  an  expanding  alkali  spot.  The  characteris- 
tic sparseness  of  the  foliage  of  the  "  alkalied  "  tree  as  compared 
with  the  adjacent  one  is  well  shown. 

Nature  of  the  injury  to  plants  from  Alkali. — When  we 
examine  plants  that  have  been  injured  by  alkali,  we  will  mostly 
find  that  the  visible  damage  has  been  done  near  the  base  of  the 
trunk,  or  root  crown;  rarely  at  any  considerable  depth  in  the 
soil  itself.  In  the  case  of  green  herbaceous  stems,  the  bark  is 
found  to  have  been  turned  to  a  brownish  tinge  for  half  an  inch 
or  more,  so  as  to  be  soft  and  easily  peeled  off.  In  the  case  of 
trees,  the  rough  bark  is  found  to  be  of  a  dark,  almost  black, 
tint,  and  the  green  layer  underneath  has,  as  in  the  case  of 
herbaceous  stems,  been  turned  brown  to  a  greater  or  less  extent. 
In  either  case  the  plant  has  been  practically  "  girdled,"  the 
effect  being  aggravated  by  the  diseased  sap  poisoning  more  or 
less  the  whole  stem  and  roots.  The  plant  may  not  die,  but  it 
•will  be  quite  certain  to  become  unprofitable  to  the  grower. 

It  is  mainly  in  the  case  of  land  very  heavily  charged  with 


ALKALI  SOILS. 


427 


v 


428  SOILS. 

common  salt,  as  in  the  marshes  bordering  the  sea,  or  salt  lakes, 
that  injury  arises  from  the  direct  effects  of  the  salty  soil-water 
upon  the  feeding  roots  themselves.  In  a  few  cases  the  grad- 
ual rise  of  salt  water  from  below  in  consequence  of  defective 
drainage,  has  seriously  injured,  arid  even  destroyed,  old  orange 
orchards.  The  natural  occupancy  of  the  ground  by  certain 
native  plants  may  be  held  to  indicate  that  the  soil  is  too 
heavily  charged  with  saline  ingredients  to  permit  healthy  root 
growth  or  nutrition  until  the  excess  of  salts  is  removed.  (See 
below,  chapters  23  and  26). 

The  fact  that  in  cultivated  land  the  injury  is  usually  found 
to  occur  near  the  surface  of  the  soil,  concurrently  with  the 
well-known  fact  that  the  maximum  accumulation  of  salts  at 
the  surface  is  always  found  near  the  end  of  the  dry  season, 
indicates  clearly  that  this  accumulation  is  due  to  evaporation 
at  the  surface.  The  latter  is  often  found  covered  with  a 
crust  consisting  of  earth  cemented  by  the  crystallized  salts, 
and  later  in  the  season  with  a  layer  of  whitish  dust  resulting 
from  the  drying-out  of  the  crust  first  formed.  It  is  this  dust 
which  becomes  so  annoying  to  the  inhabitants  and  travelers  in 
alkali  regions,  when  high  winds  prevail,  irritating  the  eyes  and 
nostrils  and  parching  the  lips. 

Effects  of  Irrigation. — One  of  the  most  annoying  and  dis- 
couraging features  of  the  cultivation  of  lands  in  alkali  regions 
is  that,  although  in  their  natural  condition  they  may  show 
but  little  alkali  on  their  surface,  and  that  mostly  in  limited 
spots,  these  spots  are  found  to  enlarge  rapidly  as  irrigation  is 
practiced.  Yet  since  alkali  salts  are  the  symptoms  and  result 
of  insufficient  rainfall,  irrigation  is  a  necessary  condition  of 
agriculture  wherever  they  prevail.  Under  irrigation,  neigh- 
boring spots  will  oftentimes  merge  together  into  one  large  one, 
and  at  times  the  entire  area,  once  highly  productive  and  perhaps 
covered  with  valuable  plantations  of  trees  or  vines,  will  become 
incapable  of  supporting  useful  growth.  This  annoying 
phenomenon  is  popularly  known  as  "  the  rise  of  the  alkali  "  in 
the  western  United  States,  but  is  equally  well  known  in  India 
and  other  irrigation  regions. 

The  soil  being  impregnated  with  a  solution  of  the  alkali 
salts,  and  acting  like  a  wick,  the  salts  naturally  remain  behind 
on  the  surface  as  the  water  evaporates,  the  process  only  stop- 


ALKALI  SOILS.  429 

ping  when  the  moisture  in  the  soil  is  exhausted.  We  thus  not 
infrequently  find  that  after  an  unusually  heavy  rainfall  there 
follows  a  heavier  accumulation  of  alkali  salts  at  the  surface, 
while  a  light  shower  produces  no  perceptible  permanent  effect. 
We  are  thus  taught  that,  within  certain  limits,  the  more  water 
evaporates  during  the  season  the  heavier  will  be  the  rise  of  the 
alkali ;  provided  that  the  water  is  not  so  abundant  as  to  leach 
the  salts  through  the  soil  and  subsoil  into  the  subdrainage. 

Leaky  Irrigation  ditches. — Worst  of  all,  however,  is  the 
effect  of  irrigation  ditches  laid  in  sandy  lands  (such  as  are 
naturally  predominant  in  arid  regions),  without  proper  pro- 
vision against  seepage.  The  ditch  water  then  gradually  fills 
up  the  entire  substrata  so  far  as  they  are  permeable,  and  the 
water-table  rises  from  below  until  it  reaches  nearly  to  the  ditch 
level;  shallowing  the  subsoil,  drowning  out  the  deep  roots  of 
all  vegetation,  and  bringing  close  to  the  surface  the  entire  mass 
of  alkali  salts  previously  diffused  through  many  feet  of  sub- 
strata. 

Surface  and  Substrata  of  Alkali  Lands. — Aside  from  the 
desert  proper,  in  the  greater  portion  of  the  alkali  country 
"  alkali  spots."  /'.  c.  ground  covered  with  saline  efflorescences 
and  showing  little  or  no  vegetation,  are  interspersed  with  larger 
areas  apparently  free  from  salts  and  covered  with  the  ordinary 
vegetation  of  the  region.  A  view  of  such  country  is  given  in 
a  plate  on  a  previous  page.  The  alkali  spots  are  usually  some- 
what depressed  below  the  surrounding  lands,  and  after  rains 
remain  covered  with  water  for  some  time:  the  water  frequently 
assuming  a  brown  or  blackish  tint  after  standing. 

\Yhen  a  pointed  steel  probe  is  pushed  down  within  such  an 
alkali  spot,  it  will  usually  be  found  that,  although  the  soil  may 
appear  quite  sandy,  it  is  penetrated  with  some  difficulty:  while 
outside  of  the  spots,  the  probe  does  not  encounter  serious  re- 
sistance until  it  reaches  the  depth  of  two  or  three  feet,  when  it 
frequently  becomes  impossible  to  penetrate  farther  without 
the  aid  of  a  hammer.  On  the  margin  of  the  spots,  the  transi- 
tion from  utter  barrenness  to  a  luxuriant  vegetation  of  native 
weeds  is  mostly  quite  sudden ;  as  is  shown  in  the  figure,  p.  425. 

Vertical  Distribution  of  the  Salts  in  Alkali  Land. — The  re- 
sults of  a  comparative  examination  of  such  land  before  and 


430 


SOILS. 


after  irrigation,1  are  shown  in  the  annexed  diagrams;  in  which 
the  kind  and  amount  of  salts  is  shown  for  every  three  inches  of 
vertical  depth,  down  to  four  feet,  by  curves  whose  extension 
from  left  to  right  indicate  the  several  percentages,  while  the 
outer  curved  line  gives  the  total  of  salts  for  each  of  the  several 
depths. 

Fig.  63  represents  the  condition  of  the  salts  in  an  "  alkali  spot"  as 
found  at  the  end  of  the  dry  season  at  the  Tulare  substation,  California. 
The  soil  was  sampled  to  the  depth  of  two  feet  at  intervals  of  three 
inches  each.  It  is  easy  to  see  that  at  this  time  the  bulk  of  the  salts 
was  accumulated  within  the  first  six  inches  from  the  surface,  while 
lower  down  the  soil  contained  so  little  that  few  culture  plants  would  be 
hurt  by  them. 

How  Native  Plants  Lire. — Fig.  64  represents  similarly  the  state  c' 
things  in  a  natural  soil  alongside  of  the  alkali  spot,  but  in  which  the 
native  vegetation  of  brilliant  flowers  develops  annually  without  any 
hindrance  from  alkali.  Samples  were  taken  from  this  spot  in  March, 
near  the  end  of  the  wet,  and  in  September,  near  the  end  of  the  dry 
season,  and  each  series  fully  analyzed.  There  was  scarcely  a  noticeable 
difference  in  the  results  obtained.  It  is  seen  in  the  figure  that  down  to 
the  depth  of  15  inches  there  was  practically  no  alkali  found  (0.035%), 
and  it  was  within  these  15  inches  of  soil  that  the  native  plants  mostly 
had  their  roots  and  developed  their  annual  growth.  But  from  that 
level  downward  the  alkali  rapidly  increased,  and  reached  a  maximum 
(0.529%),  at  about  33  inches;  decreasing  rapidly  thence  until,  at  the 
end  of  the  fourth  foot  in  depth,  there  was  not  more  alkali  than  within 
the  first  foot  from  the  surface.  In  other  words,  the  bulk  of  the  salts 
had  accumulated  at  the  greatest  depth  to  which  the  annual  rainfall 
(7  inches)  ever  reaches,  forming  there  a  sheet  of  tough,  intractable  clay- 
hardpan.  The  shallow- rooted  native  plants  germinated  their  seeds  freely 
on  the  alkali-free  surface ;  their  roots  kept  above  the  strongly-charged 
subsoil,  and  through  them  and  the  stems  r.nd  foliage  all  the  soil  mois- 
ture was  evaporated  by  the  time  the  plants  died.  Thus  no  alkali  was 
brought  up  from  below  by  evaporation.  The  seeds  shed  would  remain 
uninjured,  and  would  again  germinate  the  coming  season. 

1  Ililgard  and  Loughridge,  Bulletin  Xo.  128,  California  Experiment  Station;  Re- 
port California  Experiment  Station,  1894-9;,  p.  37  ;  Bulletin  Xo.  30,  Office  ot 
Experiment  Stations;  \Vollny's  Forsch.  Geb.  Agr.  Phys.,  1896. 


ALKALI  SOILS. 


431 


fr-nf  • 


SOILS. 


ALKALI  SOILS. 


433 


It  is  thus  that  the  luxuriant  vegetation  of  the  San  Joaquin 
plains,  dotted  with  occasional  alkali  spots,  is  maintained ;  the 
spots  themselves  being  almost  always  depressions  in  which 
the  rain  water  may  gather,  and  where,  in  consequence  of  the  in- 
creased evaporation,  the  noxious  salts  have  risen  to  the  surface 
and  render  impossible  all  but  the  most  resistant  saline  growth ; 
particularly  when,  in  consequence  of  maceration  and  fermenta- 
tion in  the  soil,  the  formation  of  carbonate  of  soda  has  caused 
the  surface  to  sink  and  become  almost  water-tight. 

Upward  Translocation  from  Irrigation. — Fig.  65  shows  the 
corresponding  profile  of  the  same  soil  after  several  years'  irri- 
gation. The  upward  movement  of  the  salts  is  clearly  seen  by 
comparison  with  the  previous  figure ;  and  the  surface  soil  has 
become  so  charged  with  salts  that  the  seeds  of  culture  plants 
refuse  to  germinate. 

Ten  feet  from  this  bare  alkali  ground,  on  which  barley  had 
refused  to  grow,  a  crop  of  barley  four  feet  high  was  harvested 
the  same  year,  without  irrigation.  Investigation  proved  that 
here  the  condition  of  the  soil  was  intermediate  between  the  two 
preceding  diagrams.  The  irrigation  water  had  dissolved  the 
alkali  of  the  subsoil,  and  the  more  abundant  evaporation  had 
brought  it  nearer  the  surface;  but  the  shading  by  the  barley 
crop  and  the  evaporation  of  the  moisture  through  its  roots 
and  leaves  had  prevented  the  salts  from  reaching  the  surface 
in  such  amounts  as  to  injure  the  crop,  although  the  tendency  to 
rise  was  clearly  shown.  By  the  use  of  gypsum,  moreover,  the 
injuriousness  of  the  alkali  had  been  somewhat  diminished. 

The  same  season,  grain  crops  were  almost  a  failure  on  alkali- 
free  land  in  the  same  region  ;  and  in  connection  with  this  result 
it  should  be  noted  as  a  general  fact  that  alkali  lands  always  re- 
tain a  certain  amount  of  moisture  perceptible  to  the  hand  dur- 
ing the  dry  season,  and  that  ////.v  moisture  can  be  utilized  b\ 
crops;  so  that  at  times  when  crops  fail  on  non-alkaline  land, 
good  ones  are  obtained  where  a  slight  taint  of  alknli  exists  in 
the  soil.  Actual  determinations  showed  that  while  a  sample  of 
alkali  soil  containing  .54%  of  salts  absorbed  12.3' 'f  of  moisture 
from  moist  air.  the  same  soil  when  leached  absorbed  only  2.5'  r 
— a  figure  corresponding  to  that  of  sandy  upland  loams. 

Alkali  in  Sand\  Lands. — In  rery  sandy  lands,  and  particu- 
larly when  the  alkali  is  "  white  "  only,  the  tendency  to  accumu- 
'  28 


434 


SOILS. 


ALKALI  SOILS. 


435 


lation  near  the  surface  is  much  less,  even  under  irrigation.  In 
the  natural  condition  the  salts  are  in  such  cases  often  found 
quite  evenly  distributed  through  soil  columns  of  four  feet,  and 
even  more.  This  is  an  additional  cause  of  the  lesser  injurious- 

0       .02      .04        06      .08        .10       12       .14-       ./6       .18      £0     .2% 


Y 


11 


Tic, .  66.— Distribution  of  Alkali  Salts  in  Sandy  Lands. 

ness  of  "  white  alkali."  An  illustration  of  the  distribution  of 
the  salts  in  very  sandy  lands,  from  the  Tulare  substation,  is 
given  in  Fig.  66.  Here  we  see  that  the  maximum  is  not  at, 
but  some  distance  below  the  surface,  the  entire  saline  mass  is 


436  SOILS. 

lower  down  than  in  the  more  clayey  loam  of  the  same  locality, 
and  is  more  widely  distributed  in  depth. 

Distribution  of  Alkali  Salts  in  Heavy  Lands. — The  mode  of 
distribution  of  alkali  salts  in  the  heavier,  close-grained  soil  of 
the  Chino  experimental  tract  in  southern  California,  is  illus- 
trated in  Fig.  67.  This  land  is  permanently  moist,  from  a 
water-table  ranging  from  five  to  seven  feet  below  the  surface 
in  ordinary  years.  There  is  therefore  no  opportunity  for  the 
formation  of  "  alkali  hardpan  "  as  in  the  case  of  the  Tulare 
soil ;  the  salts  always  remain  rather  near  the  surface,  viz.  with- 
in twelve  to  fifteen  inches.  But  being  in  much  smaller  average 
amounts  than  at  Tulare  (an  average  of  about  5300  Ibs.  per 
acre),  qui'te  a  copious  natural  vegetation  of  grasses,  sunflowers, 
and  "  yerba  mansa  "  covered  the  whole  surface,  save  in  a  few 
low  spots. 

A  similar  mode  of  distribution  of  the  salts  is  found  in  the 
still  more  clayey  "  black  adobe  "  lands  of  the  Great  Valley  of 
California.  The  scanty  rains  cannot  penetrate  these  soils  to 
any  great  depth,  so  that  evaporation  will  soon  bring  the  salts 
carried  by  them  back  to  within  a  short  distance  of  the  surface. 
Their  accumulation  there  is  frequently  indicated  by  the  entire 
absence  of  any  but  the  most  resistant  alkali  weeds,  even  though 
the  total  of  salts  in  the  land  may  not  be  very  great. 

Salton  Basin. — A  peculiar  state  of  things  is  illustrated  in  the 
Salton  Basin,  which  represents  what  was  at  one  time  the  head 
of  the  Gulf  of  California,  and  at  the  lowest  point  of  which, 
268  feet  below  sea  level,  there  now  lies  a  large  deposit  of  rock 
salt.  It  has  been  cut  off  from  the  present  Gulf  by  the  delta 
deposits  of  the  Colorado  river,  which  now,  however,  overflows 
into  the  Basin  at  times  of  extreme  high  water.  Although 
appearing  level  to  the  eye,  the  general  slope  of  the  country  is  to 
the  lowest  point  of  the  former  sea-bottom. 

The  region,  now  in  progress  of  settlement  by  means  of  irrigation 
water  brought  from  the  river  near  Yuma,  was  investigated  with  respect 
to  its  alkali  conditions  in  1900  (Bulletin  No.  140,  Calif.  Agric.  Expt. 
Sta).  The  annexed  diagram  68  shows  the  distribution  of  the  salts  to  a 
depth  of  21  feet.  It  will  be  noted  that  here  also  the  alkali  content 
becomes  insignificant  at  4  feet  depth,  but  increases  again  to  a  second 
maximum  at  about  15  feet,  below  which  there  is  a  second  decrease ; 


ALKALI  SOILS. 


437 


Fii-»t  v      foot 
Depth  of  Soil  Culuiun 


43S 


SOILS. 


ALKALI  SOILS. 


439 


below  this,  at  20  feet,  there  is  a  final  very  heavy  increase,  not  only  of 
the  total  salts  but  especially  of  common  salt,  which  evidently  represents 
the  drainage  toward  the  salt  deposit.  Above  this  level  there  is  a  very 
remarkable  predominance  of  Glauber's  salt  (sodium  sulfate),  also  observ- 
able elsewhere,  e.  g.  near  White  Plains,  Nev.,  whose  name  is  derived 
from  the  copious  surface  accumulation  of  the  sulfate.  It  seems  as 
though  this  must  have  been  formed  in  some  way  from  the  common 
salt. 

Horizontal  Distribution  of  Alkali  Salts  in  Arid  Lands. — The 
constant  occurrence  of  "  alkali  spots  "  in  arid  lands  shows  at 
once  the  great  inequality  of  horizontal  distribution  of  alkali 
impregnation.  This  is  as  prominent  in  level  lands  as  on  slopes, 
and  in  extremely  arid  regions  it  is  mostly  not  possible  to  recog- 
nize even  very  considerable  differences  without  close  examina- 
tion. Thus  in  lands  appearing  exactly  alike  on  the  surface, 
on  the  edge  of  the  Salton  basin  in  California,  on  the  same  forty 
acre  i.4(/r  (56,000  pounds  per  acre)  was  found  in  the  surface 
four  feet  at  one  point,  and  a  hundred  yards  away,  i2.5'/r 
(500,000  pounds).  The  mapping  of  alkali  lands  is  therefore 
somewhat  precarious  unless  carried  into  great  detail.  More- 
over, it  has  been  found  that  the  location  of  the  salts  changes 
from  year  to  year,  especially  in  irrigated  land,  as  might  be  ex- 
pected. Those  cultivating  alkali  lands  have  therefore  to  exer- 
cise constant  watchfulness,  unless  the  salts  have  been  defi- 
nitively eliminated  by  underdrainage  over  a  considerable  area; 
as  merely  local  operations  may  be  rendered  ineffectual  by  the 
migration  of  the  salts  from  neighboring  tracts  not  reclaimed. 

Alkuli  in  ffill  Lands. — As  a  rule,  hill  lands  themselves  are 
remarkably  free  from  alkali,  even  in  the  arid  regions;  except 
when  water  is  gathered  in  depressions,  where  strongly  saline 
waters  may  be  found  in  \Vashington.  Montana  and  elsewhere. 
But  on  level  plateau  lands,  where  drainage  is  slow  or  imperfect, 
alkali  appears  as  freely  as  it  does  in  the  same  regions  in  tiie 
stream  bottoms.  In  the  latter  the  leachings  and  seepage  ot  the 
uplands  naturally  causes  a  concentration  of  the  salts,  and  thus 
we  find  alkali  salts  incrusting  the  surface  in  the  valleys  of  the 
streams,  as  c.  £..  that  of  the  Yellowstone.  Musselshell.  Judith. 
Yakima  and  others  in  the  north,  and  of  (ireen  river.  I'latte. 
Pecos,  and  Rio  ("irande  farther  south;  as  well  as  in  numerous 
vallevs  of  central  and  southern  California. 


440 


SOILS. 


Usar  Lands  of  India. — These  lands  have  been  investigated 
first  by  the  "  Reh  Commission  "  appointed  to  investigate  the 
causes  of  the  deterioration  of  lands  in  the  Aligarh  district 
(south  of  Delhi,  between  the  Ganges  and  Jumna  rivers),  in 
1876.  The  occasion  of  this  appointment  was  the  appearance 
of  "  reh  "  (alkali  salts)  in  a  region  which  had  previously  been 
free  from  them.1  Subsequently,  a  more  elaborate  investigation 
of  the  subject  \vas  made  by  Dr.  J.  W.  Leather,  Agricultural 
Chemist  to  the  Government  of  India.2  From  these  documents 
it  appears  that  "  usar  lands  "  exist  largely  not  only  in  the 
Northwestern  Provinces  and  Oudh,  but  also  in  the  Panjab, 
especially  on  the  lands  bordering  the  Chenab  river ;  likewise  to 
a  slight  extent  in  the  Bombay  presidency.  Leather's  investi- 
gation shows  that  not  all  the  lands  designated  by  the  natives  as 
usar  contain  soluble  salts  in  injurious  amounts,  some  being 
simply  lands  having  very  hard,  clayey  soils  difficult  to  till  with 
the  imperfect  methods  employed.  Yet  the  general  phenomena 
of  the  true  "  reh  "  lands  are  practically  identical  with  those  of 
the  American  alkali  lands,  including  also  the  calcareous  hard- 
pan,  there  called  kankar.  Owing  probably  to  the  long  culti- 
vation of  the  Indian  lands  (mostly  under  irrigation),  the  salts 
are  there  at  their  maximum  in  the  first  foot,  decreasing  as 
depth  increases.  It  is  noteworthy  also  that  in  the  majority  of 
cases  the  predominant  salt  is  carbonate  of  soda  or  black  alkali, 
which  there  as  in  California  renders  the  lands  impervious  to 
water  until  treated  with  gypsum.  This  fact  accounts  for  the 
popular  use  of  the  same  name  for  non-saline  impervious  clay 
soils,  and  the  alkali  or  reh  lands  proper. 

We  have  an  entirely  analogous  case  in  the  "  Szek  "  lands  of 
the  Hungarian  plain,  some  of  which  are  simply  poor  refractory 
soils  containing  a  trace  of  soluble  salts;  while  lower  down  in 
the  valley  of  the  Theiss  we  find  genuine  alkali  lands,  both 
black  and  white,  which  have  long  furnished  carbonate  of  soda 
for  local  use  and  commerce.  In  this  case,  however,  the  alkali 
salts  seen  to  come  largely,  in  some  cases  wholly,  from  under- 
lying saline  clays  whose  salts  in  coming  to  the  surface  suffer 

1  An  abstract  of  the  report  of  this  commission  is  given  in  the  Report  of  the 
California  Experiment  Station  for  1890. 
3  See  Agricultural  Ledger,  1897,  No.  13;  ibid.  1901,  No.  13. 


ALKALI  SOILS.  44! 

precisely  the  same  transformations  experienced  in  California 
and   India,    in   presence   of    calcic   carbonate    (see   below,    p. 

450  ff). 

The  accounts  given  by  v.  Middendorff  of  the  nature  and  oc- 
currence of  alkali  lands  in  Turkestan  (Ferghana)  agree  en- 
tirely with  those  given  above  for  California  and  India;  as  do 
also  the  investigations  made  by  other  Russian  observers  on  the 
saline  lands  of  the  steppes  of  European  Russia. 

COMPOSITION   AND  QUANTITY   OF   ALKALI   SALTS. 

Black  and  White  Alkali. — Broadly  speaking,  the  world  over 
alkali  salts  consist  mainly  of  three  chief  ingredients,  already 
mentioned,  namely,  common  salt,  (ilauber's  salt  (sulfate  of 
soda),  and  salsoda  or  carbonate1  of  soda.  The  latter  causes 
what  is  popularly  known  as  "  black  alkali,"  from  the  black 
spots  of  puddles  seen  on  the  surface  of  lands  tainted  with  it, 
owing  to  the  dissolution  of  the  soil  humus;2  while  the  other 
salts,  often  together  with  Epsom  salt  and  bittern  (  Magnesium 
chlorid),  constitute  "  white  alkali,"  which  is  known  to  be  very 
much  milder  in  its  effect  on  plants  than  the  black.  In  most 
cases  all  three  are  present,  and  all  may  be  considered  as  prac- 
tically valueless,  or  noxious,  to  plant  growth. 

l\rnti'itire  Salts  in  Alkali. — \Yith  them,  however,  there  are 
almost  always  associated,  in  varying  amounts,  sulfate  of  pot- 

1  In  this  designation  are  included,  in  this  volume,  both  the  normal  (mono-)  car- 
bonate and  the  two  other  compounds,  the  bi-  or  hydrocarbonate  and  the  inter- 
mediate (so-called  sesqui-)  compound  i>r  trona;  all  of  which  are  commonly  present 
simultaneously,  but  in  utterly  indefinite  relative  proportions,  varying  from  day 
to  day  and  from  inch  to  inch  of  depth,  inasmuch  as  their  continued  existence 
depends  upon  the  greater  or  less  formation  of  carbonic  acid  in  the  soil,  and  the 
access  of  air.  Hence  their  separate  quantitative  determination  at  any  one  time  is 
of  little  practical  interest.  All  naturally  occurring  carbonate  of  soda  contains,  and 
sometimes  consists  of,  these  "  super-carbonates,"  according  to  the  greater  or  less 
exposure  to  air  and  solar  heat.  They  are  much  milder  in  their  action  on  plants 
than  the  mono  carbonate,  which  unfortunately,  in  the  nature  of  the  case,  always 
predominates  near  the  surface,  and  thus  injures  the  root-crown. 

*  A  wholly  different  kind  of  "  black  alkali  "  exists  in  some  regions,  especially  in 
the  delta  lands  of  the  Colorado  of  the  West  and  in  the  1'ecos  and  Rio  ('.ramie 
country  in  New  Mexico.  In  these  cases  the  dark  tint  is  due.  not  to  a  humic 
solution,  but  simply  to  moisture,  which  is  tenaciously  retained  by  the  chlorids  of 
calcium  and  magnesium  impregnating  the  land,  thus  contrasting  strongly  with  the 
gray  tint  of  the  general  dry  soil. 


442 


SOILS. 


•  >0    txtx    .     . 

O 

'  'BUOJJ, 
UEZZ3J 

:  °"o>     j  • 

8 

TOO    -    t^    .  OO 

8 

•sSiiuiIg 

R-  :  :  :*S>-g  

< 
•~J 

Knr 

CO     . 

8 

z 

o 

pOOMUOJJOf) 

o...t~.»«    

•     •     .  00                  ..... 

X 
I* 
<; 

H 

> 

.    co  l^  0     •     • 

-  oo  t>-  ^  •    • 

0 

5 

o 
£ 

•n^D 

5!^:  :2S!?:  :  :  :  : 

W 

sl 

I 

W 

UBiujiMAv 

H  £ 

.*««.. 

o 

< 
> 

O 

•    (?^N  °5"     •      • 

8 

TCilnix 

°-     -(g--  :  :  :  :  : 

'UE333Q 

:•?  :^  :  : 

O 

'5(33J3  UIEU 

O     ^             .     «     N    fO     

j»±iS 

.     Q-     .       . 

•133  J    S'l 

•   in  O-O     .     • 

q 

?  :      :  ^^.^  :  :  5-<S  : 

:Ts 

•iXSr 

.    LTI  N    ~     .     . 

8 

[Eua   wj 

-     •          •  ao        -     •     •  oc   N     • 

sS 

•J33}  9 

.  «,00     •     - 

o 

"Buy  EJUEg 

- 

•qjESi[V 

.   »no    r^    .     . 

8 

JE3U  'J3IS 

"1!       O 

"    JS3-V^ 

-  o  q  q-  .    • 

o 

8 

•onip 

-JBU43a     "Eg 

< 

AE3U     'SlUnj-j 

co 

< 

,,'VHV3 

I    ,        VHHHH 

•    •  ^°£    •    • 

O 

•nE3JE[,T 

.     C7-     •    ro     .    f>  £  0      •      '       •      ' 

•K30V 

2 

<. 

3ABCOJV 

:  °  :5  :  -  S-  :  :  |  : 

:  •?  q  «  :  : 

S 

§ 

:  ?  :  3.  :  a  s,  :  5>  :  :  : 

2        cr! 

|"    M  :  : 

2 

x 

UJ3M 

•   O     •  sc     .CO     ;   O     ; 

~ 

<  *-*, 

.  -,  -  1-  .  . 

o 

< 

•    -aaEinr 

.   ^    .  -y:  ^  cc   ^  vn    .     •     •   - 

CJ<^ 

2^5 

I"2"!  ; 

§ 

u 

|'U^ 

:«  :^2-?>rN  :  :  :  " 

«     < 

<       CO 

.   ^  r.0     .     • 

q 

u 

:«  :  :  :R.<§,^^  :  :  : 

.      «      «      t>.       .         . 

§ 

[3     EHES!A 

•  «    •    *    |  <o                 ;    ;    ; 

o 

.     .     .    0      .    ft    Q  M            ... 

W 

a, 
O 

2       . 

<       ~ 

£2? 
<  <  ^ 

•ESOO™ 

:  "  8-  *  "  : 

3 

uinbEoJ"  uBg 

;;;-;-""    III 

(A 

S 

c  j  « 

2SH.2 

.   n   -   r.    .     . 

0 

:::£•<*  S»§.  5     •  •  • 

W 

uizDSjqaQ 

;  ^^i; 

8 

pS 

:  .  :  "*"  "  ^?  "  "*     •  '•  '• 

J  :  5  :  Z'    " 

i; 

2|xrjz  ? 

g 

* 
i 
1 

^l|jjl'^ 

^ 

3 

Ux'^^.r"|3  2  =2~s  c 

1 

J) 

4 

llllllllllll 

P.  X  X  jr.  •/.  '_/  < 

% 

(Xi.i,xxxxxSoS< 

ALKALI  SOILS. 


443 


ai 

•uSSr 

•    O>     •      .00    <H     >" 

8 

•< 

te 
M 

>»«M 

:*  :  :N!?- 

8 

o 

s 

•< 

M 

:«*  :  :5o  . 

8 

fc 

S 

J 

:S  :  :  S-S1  : 

8 

O 
> 
> 

K 

•nouEjg 

;  o-  •  •  -o  •  • 

8 

IB 

•  00     •     •    -     •     • 

8 

Si 

.  r*   •  oo  »n  •    • 

•    ~      •    O'CO     •      • 

8 

jj 

•J.ARI 

.     M        .MOO       •        • 

3 

& 

C/J 

•3JU3pU3d9pU{ 

•  tZ.  •  n  ***   •    ^ 

8 

3 

H 

a 

-5S 

•    S    •    S°S     •     • 

8 

:S  r^sS-  :  : 

8 

Q 
< 

•pEq 

•  so      •  CO  sn      *     * 

8 

10°     "'I3"""10 

jo  :*«  :  : 

8 

o 
o 

>• 
u 

j 

J 
K 
< 

-8I«0 

•  in    •  •£>  oo     •     • 

8 

Q 

O 

:  S,  :  ?^  :  : 

8 

X 

w 

< 

t* 

O 

•II3M 

:  •§.  :  8  S  :  : 

3 

> 

W 

M 

•  CO      •    iT  ^     •      • 

8 

of, 

^ 

R 

o 

-son 

:  so1  •  2  53  '.  '. 

5 

a 

< 

•    i^l    •    t^CC      •      • 

8 

w 
fc 

H 

d, 

13 
U 

•J3[3 

:£  :~S  S  :  : 

8 

:-:*":: 

8 

(^ 

J 
J 

-M3JIV 

'.          .  >o   m    •     • 

8 

•A-3,IEA 

O   r-~    •    o^  "-1    •     • 

8 

& 

•puom 

•    -      •'  0    0-    •      • 
.  xD     •  O   r^    •     • 

3 

'5I99J'")      S  JJOQOM 

tOsO_     •    «sO      •      • 

8 

a 

:  s  :  5,  «  :  : 

8 

a 

o  o    •  -  co  <N    • 

8 

•pjo^ 

^SK?^^1 

3 

< 

> 

00    t^    •                j-i     - 

8 

IT  t  ""  ~  J  *°  •* 

8 

55 
•< 

K 

•J3AIH 

f;^  :  :  £!>  : 

8 

6 

0     -CO  SO     M^      •       • 

8 

X 

O 

ung  uo  pjo>j 

"~  :  :°-  : 

8 

Q 
•< 

XnooH 

°sS""^:  : 

8 

«5 

D4 

•wwpH  'ureirf 

o"°Si  :  :  3  J  . 

8 

O 
_! 

•uoij 

:  S1  &%  :  :  : 

8 

a. 

«»d    4VM 

"  ?  '  '.  ^^  '. 

8 

0 

u 

:  «"  *  :  :  : 

8 

•SHIAMJUO 

ft  £  S  :  ?  J?  : 

8 

•J3AU3(I 

;    0.    ;  ^g     ;     •     ; 

\ 

(H  vD    Os     •    t^  •«•     . 

g 

•     f»l      -  SO       •       •       • 

a 

unossijv    ascldn 

p>^u  :X.J 

S'ijri-Jr.'J-.'Si'S.S* 

"^  5  u  r  c  c  — 
«£  x  v:  x  S  S  2 

444  SOILS. 

ash,  phosphate  of  soda,  and  nitrate  of  soda,  representing  the 
three  elements — potassium,  phosphorus,  and  nitrogen — upon 
the  presence  of  which  in  the  soil  in  available  form,  the  welfare 
of  our  crops  so  essentially  depends,  and  which  we  aim  to  supply 
in  fertilizers.  The  potash  salt  is  usually  present  to  the  extent 
of  from  5  to  20  per  cent  of  the  total  salts ;  phosphate,  from  a 
fraction  of  one  to  as  much  as  4  percent;  the  nitrate  from  a 
fraction  of  one  to  as  much  as  20  percent.  In  black  alkali  the 
nitrate  is  usually  low,  the  phosphate  high ;  in  the  white,  the  re- 
verse is  true.  Both  relations  are  readily  intelligible  from  a 
chemical  and  bacteriological  point  of  view. 

Estimation  of  Total  Alkali  in  Land. — The  investigations 
detailed  above  having  shown  that  in  California  at  least,  out- 
side of  the  axes  of  valleys  no  practically  important  amount  of 
alkali  salts  is  usually  found  at  a  depth  exceeding  four  feet,  it 
became  possible  to  determine  approximately  the  amounts  of 
salts  that  would  have  to  be  dealt  with  when  irrigation  and 
evaporation  should  bring  the  entire  amount  to  or  near  the  sur- 
face; a  necessary  prerequisite  to  the  determination  of  possible 
cultures.  While,  as  already  shown,  the  salts  occur  lower  down 
in  very  sandy  lands,  yet  the  diagram  on  p.  435  shows  that  even 
then,  an  estimate  on  this  basis  would  not  be  very  wide  of  the 
truth.  It  is  at  least  probable  that  the  same  is  measurably  true 
of  level  alkali  lands  elsewhere,  when  not  underlaid  by  geologi- 
cal deposits  impregnated  with  salts. 

The  total  amount  of  these  salts  ordinarily  found  in  alkali 
lands  (i.  e.  in  such  as  in  the  dry  season  show  saline  efflores- 
cences on  the  surface)  is  from  about  one  tenth  of  one  per  cent 
to  as  much  as  three  per  cent  of  the  weight  of  the  soil,  taken  to 
the  depth  of  four  feet.  The  percentage  of  salts  having  been 
determined  in  samples  representing  a  tract,  it  becomes  easy  to 
calculate,  approximately,  the  total  amounts  of  each  salt  present 
per  acre,  on  the  basis  of  the  weight  of  the  soil  per  acre  foot. 
For  the  soils  of  the  arid  region,  such  weight  will  usually  range 
from  three  million  five  hundred  thousand  to  four  million 
pounds  per  acre-foot;  the  latter  being  the  most  usual  figure,  of 
which  it  may  be  conveniently  remembered,  that  forty  thousand 
pounds  represent  i  per  cent.  We  are  thus  enabled  to  esti- 
mate e.  g.  the  amount  of  gypsum  required  to  neutralize  the 
carbonate  of  soda  in  the  salts,  or  the  amounts  of  valuable  nutri- 


ALKALI  SOILS.  445 

tive  ingredients — potash,  phosphoric  acid  and  nitrates — present 
in  the  land  in  the  water-soluble  form. 

As  has  been  shown  in  the  preceding  discussion,  the  analysis 
at  the  surface  foot  alone,  which  has  frequently  been  alone 
made,  gives  no  definite  clew  whatever  to  the  total  amounts  of 
salts  to  be  controlled.  A  full  estimate  is  of  special  importance 
in  enabling  us  to  forecast  what  culture  plants  are  likely  to  suc- 
ceed on  a  given  tract,  by  reference  to  the  table  of  "  tolerances  " 
given  below  (chapter  23,  page  467). 

Composition  of  Alkali  Soils  as  a  Whole. — As  may  be  im- 
agined, the  presence  of  the  alkali  salts  finds  expression  in  the 
analytical  statement  of  their  composition,  although  not  to  the 
extent  usually  anticipated  from  their  superficial  aspect.  The 
table  annexed  gives  the  composition  of  fourteen  alkali  soils, 
taken  to  the  depth  of  one  foot,  at  times  when  there  was  no  visi- 
ble accumulation  of  salts  on  the  surface.  The  averages  of  the 
several  ingredients  determined  are  given  in  the  fifteenth  col- 
umn, and  a  comparison  of  its  figures  with  those  of  the 
general  table  on  page  377  of  chapter  20  will  show  some 
marked  characteristics.  We  find  the  average  potash-content 
to  be  but  little  less  than  twice  as  great  as  in  the  general  average 
for  the  state  of  California  ;  in  the  case  of  lime  the  ratio  is  nearly 
as  one  to  three,  in  the  case  of  magnesia  nearly  one  to  two;  in 
that  of  phosphoric  acid,  one  to  two  and  a  half,  of  which  in  the 
presence  of  carbonate  of  soda  an  unusually  large  proportion  is 
in  a  readily  soluble,  often  in  the  water-soluble,  condition  (see 
preceding  table). 

The  usual  proportion  of  soda,  of  one-fourth  to  one-half  of 
the  amount  of  potash,  is  changed  to  one-half  or  three-fourths; 
in  the  case  of  the  strongest  alkali  lands  soda  may  equal  or  even 
exceed  the  potash  content.  As  the  latter,  however,  is  in- 
variably high  to  very  high,  it  does  not  happen  as  frequently  as 
might  be  supposed  that  the  soda  content  exceeds  that  of  potash 
as  shown  by  the  usual  method  of  soil-extraction  with  water. 

That  the  potash  percentage  should  always  be  high  in  alkali  lands,  is 
hardly  surprising  when  it  is  considered  that  the  continued  presence  of 
the  salts  resulting  from  rock  decomposition  affords  opportunity  for  the 
full  exercise  of  the  preference  with  which  potash  is  known  to  be  retained 


446 


SOILS. 


o  oo  "ivo  o  o 


.      . 

00   co    .     .         O 


E.2 


" 


nt,  i 
nt,  in 


Chlorins  pe 
Humus 
"  Ash 
"  Nitro 
"  " 
Hygroscopic 
bsorbed  a 


ALKALI  SOILS. 


447 


6 
5^ 

o-o 


U.>ro  £ 

l*ur 

t/;  — 


;e 


H  o*  t^  t-*  c  en  « 


c  o 

31   I 

is? 

UW 


C.3 


M  ;/;  £<  u:  ~  «s  s:  s»  <  a.  i/: 


lori 
mu 

gro 

bso 


448  SOILS. 

in  soils  by  the  formation  of  complex  zeolitic  silicates.  In  most  cases 
the  potash-percentage  exceeds  .75%,  and  rises  as  high  as  2.0^  ;  as  is 
shown  in  the  table. 

This  table  exhibits  also  another  standing  characteristic  of 
alkali  soils,  which  is  to  be  anticipated  from  the  conditions  of 
their  formation ;  viz,  high  lime-content,  which  sometimes  rises 
to  the  extent  of  marliness. 

In  phosphates,  also,  alkali  soils  are  almost  always  high ;  and 
an  unusually  large  proportion  is  found  to  be  readily  soluble. 

In  presence  of  much  carbonate  of  soda,  nitrates  are  usually 
scarce  or  altogether  absent;  while  owing  to  the  action  of  the 
alkaline  solution  upon  the  humus,  ammonia  salts,  or  even  free 
(or  carbonated  and  therefore  readily  dissociated  and  assimi- 
lated) ammonia  may  be  present,  so  as  to  be  perceptible  to  the 
senses  by  its  odor  in  hot  sunshine.  But  in  the  case  of  "  white 
alkali,"  more  especially  of  the  sulphate  in  moderate  amounts, 
nitrification  is  exceedingly  active  and  nitrates  may  sometimes 
rise  to  as  much  as  20%  of  the  soluble  salts.  As  alkali  spots  are 
usually  low  in  the  central  portion  and  therefore  more  moist 
than  around  the  edges,  we  sometimes  find  ammonia  salts  in  the 
middle  of  a  spot,  while  nitrates  are  abundant  along  the  mar- 
gin of  the  same.  These  differences,  first  demonstrated  by  an 
investigation  made  by  Colmore,1  illustrate  some  of  the  reac- 
tions that  are  essentially  concerned  in  the  agricultural  avail- 
ability of  alkali  lands.  A  summary  of  Colmore's  results  is 
given  in  the  table  below. 

Cross  Section  of  an  Alkali  Spot. — The  spot  examined  lies 
outside  of  Tulare,  California,  substation;  it  being  late  in  the 
season,  when  the  bulk  of  the  salts  is  found  near  the  surface, 
the  samples  were  taken  to  the  depth  of  one  foot  only,  at  points 
four  feet  apart,  from  the  center  out. 

1  Report  of  the  California  Exp't  St'n  for  1892-94,  p.  141. 


ALKALI  SOILS.  449 

AMOUNT  AND  COMPOSITION   OF  SALTS  IN  ALKALI   SPOT  FROM  CENTER  TO 
CIRCUMFERENCE,  4  FEET  APART,   I    FT.   DEPTH. 


Mineral  Salts. 

I 

Center 
of  spot. 

2 

Four 
feet. 

3 

Eight 
feet. 

4 

Twelve 
feet. 

5 

Outer 
margin. 

Potassium  sulfate  

6.70 

q.  cc 

I  1.  02 

19.26 

I  7  OS 

Sodium  sulfate      .  .      . 

10  84 

128; 

27  T1 

Magnesium  sulfate  

-3  O7 

O7 

nc 

^  oc 

8  ->a 

Sodium  chlorid                  .  .        ... 

1  7.80 

2777 

24  I  *> 

2/1.21 

20  60 

Sodium  carbonate  

<;o  72 

CO  06 

77.  cc 

7?  4O 

2O  Q4 

Sodium  phosphate  

C.C7 

2.88 

.87 

1  .04 

Sodium  nitrate  

.TO 

? 

.87 

> 

1  1 

Totals  

IOO  OO 

IOO  OO 

IOO  OO 

IOO  OO 

IOO  OO 

Organic  matter  

30  oo 

24.80 

10.48 

27  76 

2O  71 

Total  soluble  in  soil  

.78 

.  c.4 

7O 

77 

74 

Mineral  salts  

.•$ 

.40 

C4, 

,2C 

.27 

While  the  table  shows  an  obvious  irregularity  in  some  of  the  data  at 
the  eight-foot  point,  arising  doubtless  from  an  irregularity  of  surface  or 
of  texture  overlooked  in  taking  the  samples,  we  find  a  very  remarkable 
regularity  of  progression  in  the  cases  of  potassium  sulfate,  sodium 
chlorid,  sodium  carbonate  and  sodium  phosphate  in  the  other  four 
samples.  The  maxima  of  the  "  black  alkali  "  and  the  soluble  organic 
matter  (humus)  coincide,  as  does  that  of  the  phosphate ;  the  total 
mineral  salts  at  the  outer  margin  are  only  a  little  over  half  of  what  is 
found  at  the  center.  This  is  natural,  as  owing  to  the  deflocculating 
effect  of  the  black  alkali,  the  center  is  nearly  a  foot  lower  than  the 
margin.  The  lowering  of  the  nitrate-content  at  the  outer  margin  is 
obviously  due  to  the  luxuriant  vegetation  growing  adjacent. 

Reactions  betiveen  the  Carbonates,  Chlorids  and  Sulfatcs  of  Alkalies 
and  Earths.  That  a  soluble  earth-salt,  such  as  the  sulfate  or  chlorid  of 
calcium,  will  react  upon  an  alkaline  carbonate  solution  so  as  to  form  an 
alkali  sulfate,  and  e.g.  lime  carbonate,  is  well  known;  the  neutralization 
of  the  sodic  carbonate  in  the  soil  by  means  of  gypsum,  above  referred 
to,  is  based  upon  this  reaction.  It  is  not  so  well  known  that  the  latter 
may  be  reversed,  partly  or  wholly,  by  the  presence  of  carbonic  acid  in 
the  solution  of  the  soil.  Although  observed  as  early  as  1824  by  Brandes, 
and  again  in  1859  by  A.  Miiller,  this  reaction  is  not  mentioned  in  text- 
books and  attracted  no  attention  as  a  source  of  naturally  occurring 
alkali  carbonates  which  in  the  past  have  formed  the  basis  of  extensive 
commerce  from  the  Orient,  until  in  iS8S,  the  writer  together  with  Weber 
29 


450 


SOILS. 


and  later  with  Jaffa,  investigated  it  quantitatively.1  It  was  found  that 
up  to  .75  grms.  per  liter,  the  entire  amount  of  sodic  sulfate  present  in 
solution  is  transformed  into  carbonate  in  presence  of  calcic  carbonate, 
by  a  current  of  carbonic  dioxid ;  but  the  amount  so  transformed  does 
not  continue  to  increase  beyond  about  4  grams  per  liter.  A  correspond- 
ing amount  of  calcic  sulfate  is  formed.  In  the  case  of  potassic 
sulfate,  the  transformation  also  occurs,  proportionally  to  the  molecular 
weight.  This  relation  is  shown  in  the  subjoined  diagram,  which  also 
shows  in  the  curves  on  the  left,  the  residual  alkalinity  left  after  evapora- 
tion and  drying  the  residue  at  100°  C. 


01      234567 


Grams  per  Efter  KHCOS 
9     10    11     12    13    U     15    16    17   18    19    20    21    22    23    24    25     29 


FIG.  6g.— Progressive   Transformation  of   Alkali   Sulfates  into  Carbonates.     (The   figures  along 
upper  line  represent  tenths  of  one  per  cent.) 

The  corresponding  reaction  occurs  also,  of  course,  between 
sodium  chlorid  and  calcium  carbonate,  but  not  to  the  same 
extent,  because  unlike  the  difficultly  soluble  gypsum,  the  reac- 
tion product  is  the  very  soluble  calcium  chlorid,  the  presence  of 
which  in  the  solution  limits  the  reaction  much  sooner  than 
when  most  of  the  decomposition  product  is  thrown  down  in 

1  Proc.  Am.  Soc.  Agr.  Sci.,  1888  ;  ibid.,  1890;  Rep.  Cal.  Expt.  Sta.,  1890,  p.  100; 
Ber.  Berlin,  Chem.  Ges.,  1893;  Am.  Jour.  Sci.,  August  1896. 


ALKALI  SOILS,  451 

the  solid  state.  The  calcium  chlorid  not  uncommonly  found  in 
some  alkali  regions  is  undoubtedly  the  product  of  the  above  re- 
action. 

As  the  saline  solutions  in  the  soil  are  mostly  quite  dilute,  and 
calcic  carbonate  is  always  present,  it  follows  that  whenever 
under  the  influences  which  favor  the  oxidation  of  organic  mat- 
ter in  the  soil,  and  the  activity  of  the  plant  roots,  carbonic  gas 
is  formed  somewhat  copiously,  alkali  sulfates  and  chlorids 
present  may  be  partially  or  wholly  transformed  into  carbonates 
within  the  soil.  As  a  matter  of  fact,  it  is  found  that  this  trans- 
formation occurs  most  readily  in  the  moister  portions  of  the 
soil  and  subsoil,  and  invariably  so  when  an  alkali  soil  is 
"  swaniped  "  by  excessive  irrigation  or  rise  of  bottom  water; 
while  the  reaction  is  again  reversed  whenever  free  access  of  air 
reduces  the  carbonic  dioxid  below  a  certain  point.  It  thus  be- 
comes intelligible  why  in  the  diagrams  showing  the  distribu- 
tion of  the  salts  (this  chapter  pp.  431  and  432),  we  always 
find  the  sodic  carbonate  relatively  decreasing  as  the  surface 
is  approached. 

Thus,  also,  is  explained  the  fact  that  sodium  carbonate  is 
formed  more  abundantly  toward  the  center  of  the  root  system 
of  alkali  plants,  such  as  the  greasewood,  beneath  which  the  soil 
is  always  more  abundantly  charged  with  "  black  alkali  "  than 
is  the  surrounding  earth. 

Good  aeration  of  the  soil  mass,  then,  is  essential  in  main- 
taining the  neutralization  of  the  "  black  alkali  ''  soils  brought 
about  by  the  use  of  gypsum  (land  plaster). 

Inverse  Ratios  of  Alkali  Carbonates  and  Sulfates. — Ac- 
cording to  the  above  considerations,  it  is  not  surprising  that 
we  should  often  find  an  apparent  inverse  ratio  between  the 
alkali  sulfates  and  carbonates  in  soils  so  closely  adjacent  that 
their  salts  must  be  presumed  to  be  similar  in  composition.  A 
striking  example  is  shown  in  fig.  70,  in  which  this  inverse  ratio 
becomes  apparent  four  times  in  succession  in  one  and  the  same 
soil  profile.  While  this  inference  is  plain  on  the  face  of  the 
diagram,  it  is  not  quite  easy  to  explain  in  detail  how  this  alter- 
nation came  about  from  the  condition  observed  two  months 
previously.  Most  probably  it  was  caused  by  corresponding 
alternations  of  weather,  in  which  short,  warm  spring  showers 
alternated  with  similarly  brief  periods  of  drying  north  winds; 


452 


SOILS. 


ALKALI  SOILS. 


453 


the  latter  causing  a  reversal  of  the  formation  of  sodic  carbonate 
that  had  been  induced  by  the  former. 

Exceptional  Conditions. — While  the  phenomena  of  alkali 
lands  as  outlined  above  probably  represent  the  vastly  predomi- 
nant conditions  on  level  lands,  yet  there  are  exceptions  due  to 
surface  conformation,  and  the  local  existence  of  sources  of 
alkali  salts  outside  of  the  soil  itself.  Such  is  the  case  where 
salts  ooze  out  of  strata  cropping  out  on  hillsides,  as  at  some 
points  in  the  San  Joaquin  Valley  in  California,  and  in  parts  of 
New  Mexico,  Colorado  and  Wyoming;  also  where,  as  in  the 
Hungarian  plain,  saline  clays  underlie  within  reach  of  surface 
evaporation. 

Again,  it  not  infrequently  happens  that  in  sloping  valleys  or 
basins,  where  the  central  (lowest)  portion  receives  the  salts 
leached  out  of  the  soils  of  the  adjacent  slopes,  we  find  belts  of 
greater  or  less  width  in  which  the  alkali  impregnation  may 
reach  to  the  depth  of  ten  or  twelve  feet,  usually  within  more  or 
less  definite  layers  of  calcareous  hardpan,  likewise  the  outcome 
of  the  leaching  of  the  valley  slopes.  Such  areas,  however,  are 
usually  quite  limited,  and  are  at  present  scarcely  reclaimable 
without  excessive  expenditure;  the  more  as  they  are  often  un- 
derlaid by  saline  bottom  water.  In  these  cases  the  predominant 
saline  ingredient  is  usually  common  salt,  as  might  be  expected 
and  as  is  exemplified  in  the  Great  Salt  Lake  of  Utah,  in  the 
Antelope  and  Ferris  Valleys,  and  in  Salton  basin  in  California; 
in  the  Yellowstone  valley  near  Billings,  Mont.1  in  the  Aralo- 
Caspian  desert,  and  at  many  other  points. 

Conclusions. — Summing  up  the  conclusions  from  the  fore- 
going facts  and  considerations,  we  find  that — 

(  i )  The  amount  of  soluble  salts  in  alkali  lands  is  usually 
limited;  they  are  not  ordinarily  supplied  in  indefinite  quantities 
from  the  bottom-water  below.  These  salts  have  mostly  been 
formed  by  weathering  in  the  soil-layer  itself. 

(2)  The  salts  move  up  and  down  within  the  upper  four  or 
five  feet  of  the  soil  and  subsoil,  following  the  movement  of  the 
moisture;  descending  in  the  rain}'  season  to  the  limit  of  the 
annual  moistening  as  a  maximum,  and  then  reascending  or  not. 
according  as  surface  evaporation  may  demand.  At  the  end  of 

1  Farmer's  Bull.  No.  83,  U.  S.  Dept.  Agr.,  1899. 


454  SOILS. 

the  dry  season,  in  untilled  irrigated  land,  practically  the  entire 
mass  of  salts  may  be  within  six  or  eight  inches  of  the  surface. 

(3)  The   direct   injury   to  vegetation1    is   caused   largely 
within  a  few  inches  of  the  surface,  by  the  corrosion  of  the  bark, 
usually  near  the  root  crown.     This  corrosion  is  strongest  when 
carbonate  of  soda  (salsoda)   forms  a  large  proportion  of  the 
salts;  the  soda  then  also  dissolves  the  vegetable  mold   and 
causes  blackish  spots  in  the  soil,  popularly  known  as  black 
alkali. 

(4)  The  injury  caused  by  carbonate  of  soda  is  aggravated 
by  its  action  in  puddling  the  soil  so  as  to  cause  it  to  lose  its 
crumbly  or  flaky  condition,  rendering  it  almost  or  quite  un- 
tillable  and  impervious.     It  also  tends  to  form  in  the  depths  of 
the  soil-layer  a  tough,  impervious  hardpan,  which  yields  neither 
to  plow,  pick,  nor  crowbar.     Its  presence  is  easily  ascertained 
by  means  of  a  pointed  steel  sounding-rod. 

(5)  While  alkali  lands  share  with  other  soils  of  the  arid 
region  the  advantage  of  unusually  high  percentages  of  plant- 
food  in  the  insoluble  form,  they  also  contain,  alongside  of  the 
noxious   salts,  considerable  amounts   of  water-soluble   plant- 
food.    When,  therefore,  the  action  of  the  noxious  salts  is  done 
away  with,  they  should  be  profusely  and  lastingly  productive ; 
particularly  as  they  are  always  naturally  somewhat  moist  in 
consequence  of  the  attraction  of  moisture  by  the  salts,  and  are 
therefore  less  liable  to  injury  from  drought  than  the  same  soils 
when  free  from  alkali. 

1  For  a  general  statement  and  discussion  of  the  physiological  effects  of  saline 
solutions  on  plants,  see  chapter  26. 


CHAPTER  XXIII. 
UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS. 

Alkali-Resistant  Crops. — The  most  obvious  mode  of  utiliz- 
ing alkali  lands  is  to  occupy  them  with  crops  not  affected  by  the 
noxious  salts.  Unfortunately  but  few  such  crops  of  general 
utility  have  as  yet  been  found  for  the  stronger  class  of  alkali 
lands.  The  question  is  always  one  of  degree,  which  frequently 
cannot  be  decided  without  an  actual  determination  of  the 
amount  and  kind  of  salts  to  be  dealt  with,  to  which  the  crops 
can  then  be  adapted  in  accordance  with  the  greater  or  less  sensi- 
tiveness of  the  several  plants,  as  indicated  in  the  table  of  toler- 
ances given  farther  on.  But  aside  from  this,  there  are  certain 
general  measures  and  precautions  which  in  any  case  will  serve 
to  mitigate  the  effect  of  the  alkali  salts.  Foremost  among 
these,  and  applicable  everywhere,  is  the  prevention  of  evapora- 
tion to  the  utmost  extent  possible. 

Counteracting  Evaporation. — Since  evaporation  of  the  soil- 
moisture  at  the  surface  is  what  brings  the  alkali  to  the  level 
where  the  main  injury  to  plants  occurs,  it  is  obvious  that  evapo- 
ration should  be  prevented  as  much  as  possible.  This  is  the 
more  important,  as  the  saving  of  soil-moisture,  and  therefore 
of  irrigation  water,  is  attainable  by  the  same  means. 

Three  methods  for  this  purpose  arc  usually  practiced,  viz., 
shading,  mulching,  and  the  maintenance  of  loose  tilth  in  the 
surface  soil  to  such  depth  as  may  be  required  by  the  climatic 
conditions. 

As  to  mulching,  it  is  already  well  recognized  in  the  alkali 
regions  of  California  as  an  effective  remedy  in  light  cases. 
Fruit  trees  are  frequently  thus  protected,  particularly  while 
young,  after  which  their  shade  alone  may  (  as  in  the  case  of 
low-trained  orange  trees)  suffice  to  prevent  injury.  The  same 
often  happens  in  the  case  of  low-trained  vines,  small-fruit,  and 
vegetables.  Sanding  of  the  surface  to  the  depth  of  several 
inches  was  among  the  first  attempts  in  this  direction;  but  the 

455 


456  SOILS. 

necessity  of  cultivation,  involving  the  renewal  of  the  sand  each 
season,  renders  this  a  costly  method.  Straw,  leaves,  and  ma- 
nure have  been  more  successfully  used;  but  even  these,  unless 
employed  for  the  purpose  of  fertilization,  involve  more  ex- 
pense and  trouble  than  the  simple  maintenance  of  very  loose 
tilth  of  the  surface  soil  throughout  the  dry  season;  a  remedy 
which,  of  course,  is  equally  applicable  to  hoed  field  crops,  and 
is  in  the  case  of  some  of  these — e.  g.,  cotton — a  necessary  con- 
dition of  cultural  success  everywhere.  The  wide  prevalence 
of  "  light  "  soils  in  the  arid  regions,  from  causes  inherent  in 
the  climate  itself,  renders  this  condition  relatively  easy  of  ful- 
filment. 

Turning-under  of  Surface  Alkali. — Aside,  however,  from 
the  mere  prevention  of  surface  evaporation,  another  favorable 
condition  is  realized  by  this  procedure,  namely  the  comming- 
ling of  the  heavily  salt-charged  surface-layers  with  the  rela- 
tively non-alkaline  subsoil.  Since  in  the  arid  regions  the  roots 
of  al!  plants  retire  farther  from  the  surface  because  of  the 
deadly  drought  and  heat  of  summer,  it  is  usually  possible  to 
cultivate  deeper  than  could  safely  be  done  with  growing  crops 
in  humid  climates.  Yet  even  there,  the  maxim  of  "  deep  prep- 
aration and  shallow  cultivation  "  is  put  .into  practice  with  ad- 
vantage, only  changing  the  measurements  of  depth  to  corre- 
spond with  the  altered  climatic  conditions.  Thus  while  in  the 
humid  States,  three  to  four  inches  is  the  accepted  standard  of 
depth  for  summer  cultivation  to  preserve  moisture  without 
injury  to  the  roots,  that  depth  must  in  the  arid  region  fre- 
quently be  doubled  in  order  to  be  effective ;  and  will  even  then 
scarcely  touch  a  living  root  in  orchards  and  vineyards,  particu- 
larly in  unmanured  and  unirrigated  land. 

A  glance  at  fig.  63,  chapt.  22,  p.  431),  will  show  the  great 
advantage  of  extra-deep  preparation  in  commingling  the  alkali 
salts  accumulated  near  the  surface  with  the  lower  soil-layers, 
diffusing  the  salts,  say  through  twelve  instead  of  six  inches  of 
soil  mass.  This  will  in  very  many  cases  suffice  to  render  the 
growth  of  ordinary  crops  possible  if,  by  subsequent  frequent 
and  thorough  cultivation,  surface  evaporation,  and  with  it  the 
re-ascent  of  the  salts  to  the  surface,  is  prevented. 

A  striking  example  of  the  efficiency  of  this  mode  of  proced- 
ure was  observed  at  the  Tulare  substation,  California,  where  a 


UTILIZATION  AND  RECLAMATION    OF  ALKALI  LANDS.     457 

portion  of  a  very  bad  alkali  spot  was  trenched  to  the  depth  of 
two  feet,  throwing  the  surface  soil  to  the  bottom.  The  spot 
thus  treated  produced  excellent  wheat  crops  for  two  years — the 
time  it  took  the  alkali  salts  to  reascend  to  the  surface. 

It  should  therefore  be  kept  in  mind  that  whatever  else  is 
done  toward  reclamation,  deep  preparation  and  thorough  culti- 
vation must  be  regarded  as  prime  factors  for  the  maintenance 
of  production  on  alkali  lands. 

The  Efficacy  of  Shading,  already  referred  to,  is  strikingly 
illustrated  in  the  case  of  some  field  crops  which,  when  once 
established,  will  thrive  on  fairly  strong  alkali  soil,  provided 
that  a  good  thick  "  stand  "  has  once  been  obtained.  This  is 
notably  true  of  the  great  forage  crop  of  the  arid  region,  alfalfa 
or  lucern.  Its  seed  is  extremely  sensitive  to  "  black  "  alkali, 
and  will  decay  in  the  ground  unless  protected  against  it  by  the 
use  of  gypsum  in  sowing.  But  when  once  a  full  stand  has  been 
obtained,  the  field  may  endure  for  many  years  without  a  sign 
of  injury.  Here  two  effects  combine,  viz.,  the  shading,  and  the 
evaporation  through  the  deep  roots  and  abundant  foliage, 
which  alone  prevents,  in  a  large  measure,  the  ascent  of  the 
moisture  and  salts  to  the  surface.  The  case  is  then  precisely 
parallel  to  that  of  the  natural  soil  (see  p.  432,  chapter  22),  ex- 
cept that,  as  irrigation  is  practiced  in  order  to  stimulate  produc- 
tion, the  sheet  of  alkali  hardpan  will  be  dissolved  and  its  salts 
spread  through  the  soil  more  evenly.  The  result  is  that  so  soon 
as  the  alfalfa  is  taken  off  the  ground  and  the  cultivation  of 
other  crops  is  attempted,  an  altogether  unexpectedly  large 
amount  of  alkali  comes  to  the  surface  and  greatly  impedes,  if 
it  docs  not  altogether  prevent,  the  immediate  planting  of  other 
crops.  Shallow-rooted  annual  crops  that  give  but  little  shade, 
like  the  cereals,  while  measurably  impeding  the  rise  of  the 
salts  during  their  growth  (see  fig.  70.  page  452)  frequently 
allow  of  enough  rise  after  harvest  to  prevent  reseeding  the 
following  season. 

"  Neutralizing  "  Black  Alkali. — Since  so  little  carbonate  of 
soda  as  one-tenth  of  one  per  cent,  may  suffice  to  render  some 
soils  uncultivable,  it  frequently  happens  that  its  mere  trans- 
formation into  the  sulfatc  is  sufficient  to  remove  all  stress  from 
alkali.  Gypsum  (land  plaster)  is  the  cheap  and  effective  agent 
to  bring  about  this  transformation,  provided  water  be  also 


458  SOILS. 

present.  The  amount  required  per  acre  will,  of  course,  vary 
with  the  amount  of  salts  in  the  soil,  all  the  way  from  a  few 
hundred  pounds  to  several  tons  in  the  case  of  strong  alkali 
spots ;  but  it  is  not  usually  necessary  to  add  the  entire  quantity 
at  once,  provided  that  sufficient  be  used  to  neutralize  the  sodic 
carbonate  near  the  surface,  and  enough  time  be  allowed  for  the 
action  to  take  place.  In  very  wet  soil,  and  when  much  gypsum 
is  used,  this  may  occur  within  a  few  days ;  in  merely  damp  soils 
in  the  course  of  months;  but  usually  the  effect  increases  for 
years,  as  the  salts  rise  from  below. 

The  effect  of  gypsum  on  black-alkali  land  is  often  very  strik- 
ing, even  to  the  eye.  The  blackish  puddles  and  spots  disappear, 
because  the  gypsum  renders  the  dissolved  humus  insoluble  and 
thus  restores  it  to  the  soil.  The  latter  soon  loses  its  hard, 
puddled  condition  and  crumbles  and  bulges  into  a  loose  mass, 
into  which  water  now  soaks  freely,  bringing  up  the  previously 
depressed  spots  to  the  general  level  of  the  land.  On  the  sur- 
face thus  changed,  seeds  now  germinate  and  grow  without  hin- 
drance ;  and  as  the  injury  from  alkali  occurs  at  or  near  the  sur- 
face, it  is  usually  best  to  simply  harrow  in  the  plaster,  leaving 
the  water  to  carry  it  down  in  solution.  Soluble  phosphates 
present  are  decomposed  so  as  to  retain  finely  divided,  but  less 
soluble  earth  phosphates  in  the  soil. 

It  must  not  be  forgotten  that  this  beneficial  change  may  go 
backward  if  the  land  thus  treated  is  permitted  to  be  swamped 
by  irrigation  water  or  otherwise.  Under  the  same  conditions 
naturally  white  alkali  may  turn  black  (see  above,  chapter  22, 
p.  451).  Of  course,  gypsum  is  of  no  benefit  whatever  on  soils 
containing  no  "black"  alkali,  but  only  ("white")  Glauber's 
and  common  salt. 

Removing  the  Salts  from  the  Soil. — In  case  the  amount  of 
salts  in  the  soil  should  be  so  great  that  even  the  change  worked 
by  gypsum  is  insufficient  to  render  it  available  for  useful  crops, 
the  only  remedy  left  is  to  remove  the  salts,  partially  or  wholly, 
at  least  from  the  surface  of  the  land.  Three  chief  methods  are 
available  for  this  purpose.  One  is  to  remove  the  salts,  with 
more  or  less  earth,  from  the  surface  at  the  end  of  the  dry 
season,  either  by  sweeping  or  by  means  of  a  horse  scraper  set 
so  as  to  carry  off  a  certain  depth  of  soil.  Thus  sometimes  in  a 
single  season  one-third  or  one-half  of  the  total  salts  may  be  got 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     459 

rid  of,  the  loss  of  a  few  inches  of  surface  soil  being  of  little 
moment  in  the  deep  soils  of  the  arid  region.  Another  method 
affording  partial  relief  is  to  flood  the  land  for  a  sufficient 
length  of  time  to  carry  the  alkali  three  or  more  feet  below  the 
surface,  then  carefully  preventing  its  reascent  by  suppressing 
evaporation  (see  this  chapter,  p.  455)  as  much  as  possible. 
The  best  of  all,  the  final  and  universally  efficient  remedy,  is  to 
leach  the  alkali  salt  out  of  the  soil  into  the  country  drainage ; 
supplementing  by  irrigation  water  what  is  left  undone  by  the 
deficient  rainfall. 

It  is  not  practicable,  as  many  suppose,  to  wash  the  salts  off 
the  surface  by  a  rush  of  water,  as  they  instantly  soak  into  the 
ground  at  the  first  touch.  Nor  is  there  any  certain  relief  from 
allowing  the  water  to  stand  on  the  land  and  then  drawing  it  off ; 
in  this  case  also  the  salts  soak  down  ahead  of  the  water,  and 
the  water  standing  on  the  surface  remains  almost  unchanged. 
In  very  pervious  soils  and  in  the  case  of  white  alkali,  the 
washing-out  can  often  be  accomplished  without  special  provis- 
ion for  underdrainage,  by  leaving  the  water  on  the  land  suffi- 
ciently long.  But  the  laying  of  regular  underdrains  greatly 
accelerates  the  work,  and  renders  success  certain. 

Lcaching-Doii.'n, — In  advance  of  underdrainage,  it  is  quite 
generally  feasible,  where  the  land  has  been  leveled  and  diked 
for  irrigation  by  surface  flooding,  to  leach  the  salts  out  of  the 
first  three  or  four  feet  by  continued  flooding,  thus  taking  them 
out  of  reach  of  the  crop  roots,  or  at  all  events  giving  the  seed 
an  opportunity  to  escape  injury  from  alkali.  This  plan  is  es- 
pecially effective  in  the  case  of  alfalfa,  the  young  seedlings  of 
which  are  very  sensitive,  while  the  grown  plant  is  rather  re- 
sistant. In  order  to  obtain  this  relief  so  as  to  know  what  is 
being  accomplished,  the  farmer  should  ascertain  beforehand 
how  fast  water  will  soak  down  in  his  ground  '}  for  in  heavy  clay 
soils,  and  especially  in  those  containing  black  alkali,  the  soak- 
age  is  sometimes  so  slow  that  the  upward  diffusion  of  the  salts 
keeps  pace  with  the  downward  soakagc ;  in  which  case  nothing 
is  accomplished  by  flooding,  and  underdrainage  is  the  only 
remedy.  But  in  most  soils  of  the  arid  region  flooding  from 
three  days  to  a  week  will  remove  the  alkali  beyond  reach  of 
the  roots  of  ordinary  crops.  If  subsequently  irrigation  is  done 

1  See  p.  242,  Chap.  13. 


460 


SOILS. 


by  means  of  deep  furrows,  the  alkali  salts  may  be  either  kept 
at  a  low  level  continuously,  or  if  the  land  be  at  all  pervious,  the 
alkali  may  ultimately  be  permanently  leached  out  into  the  sub- 
drainage  by  farther  flooding.  When  the  alkali  has  not  accumu- 
lated near  the  surface  to  any  great  extent,  irrigation  by  deep 
furrows  may,  alone,  afford  all  the  relief  needed. 

In  the  case  illustrated  by  figures  71  and  72,  irrigation  by 
shallow  furrows  with  water  too  strongly  charged  with  salts 
had  so  far  added  to  the  natural  alkali-content  of  the  land  that 


FIG.  71. — Lemon  Orchard  Affected  by  Alkali ;  Before  Deep  Irrigation. 

the  lemon  trees  were  being  defoliated.  Upon  the  advice  of  the 
California  Station  the  deep-furrow  system  was  adopted,  and 
within  two  years  the  results  were  as  shown  in  figure  72, 
the  salts  having  been  carried  down  and  diluted  so  as  to  be- 
come harmless. 

Undcrdrainagc  the  Final  and  Universal  Remedy  for  Alkali. 
—When  we  underdrain  an  alkali  soil,  we  adopt  the  very  means 
by  w-hich  the  existence  of  alkali  lands  in  the  humid  regions  is 
wholly  prevented ;  the  leaching-out  of  the  soluble  salts  formed 
in  soil-weathering  as  fast  as  they  are  formed.  The  long  and 
abundant  experience  had  with  underdrainage  in  reclaiming 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     461 

saline  sea-coast  lands,  applies  directly  and  cogently  to  alkali 
lands.  It  is  the  universal  remedy  for  all  the  evils  of  alkali, 
and  its  only  drawback  is  the  first  expense,  and  the  necessity  for 
obtaining  an  outlet  for  the  drain  waters,  which  cannot  always 
be  had  on  the  owner's  land.  Hence  it  requires  co-operation  or 
legislation  to  render  the  great  improvement  of  underdrainage 
feasible.  Such  legislation  is  well  established  in  the  old  world, 
and  has  been  enacted  in  several  states  even  of  the  humid 
region.  Where  irrigation  is  practiced  as  a  matter  of  necessity, 


I' ic..  12.  -The  Above  Orchard  after  Alkali  was  Driven  Down  by  Deep  Irrigation,  followed  by 

Cultivation. 

underdrainage  is  a  correlative  necessity,  both  to  avoid  the  evils 
of  over-irrigation  and  to  relieve  the  land  of  noxious  alkali 
salts. 

The  drainage  law  now  existing  in  California  does  not  go 
farther  than  to  authorixe  the  formation  of  drainage  districts. 
within  which  the  necessary  taxes  may  be  levied  ;  and  there  is 
some  difficulty  in  securing  popular  action.  P>ut  bitter  experi- 
ence will  doubtless  in  time  comj)el  unanimity,  such  as  now  ex- 
ists, c.  g..  in  Illinois,  where  drainage  is  not  nearly  so  urgently 
needed  as  it  is  in  the  irrigation  States. 


462 


SOILS. 


Possible  Injury  to  Land  by  Excessive  Leaching. — It  should 
not  be  forgotten,  however,  that  excessive  leaching  of  under- 
drained  land  by  flooding  is  liable  to  injure  the  soil  in  two 
ways :  first,  by  the  removal  of  valuable  soluble  plant-food ;  and 
further,  by  rendering  the  land  less  retentive  of  moisture,  such 
retention  being  favored  by  the  presence  of  small  amounts  of 
alkali  salts,  not  sufficient  to  injure  crops.  After  the  salts  have 
been  carried  down  to  a  sufficient  depth  to  prevent  injury  to 
annual  crops,  and  with  proper  subsequent  attention  to  the  pre- 
vention of  surface  evaporation,  the  flooding  will  not  need  to 
be  repeated  for  several  years.  Thus  in  many  soils  excellent 
crops  may  be  grown  even  in  strong  alkali  land,  pending  the 
establishment  of  permanent  drainage  systems. 

The  importance  of  thoroughly  washing  the  alkali  deeply  into  the 
soil  before  the  seed  is  planted,  and  keeping  it  there  by  proper  means 
until  the  foliage  of  the  plant  shades  the  soil  sufficiently  to  prevent  the 
rise  of  moisture  and  alkali,  is  well  illustrated  in  fields  in  the  region  of 
Bakersfield,  Cal.,  where  alfalfa  is  now  growing  in  soils  once  heavily 
charged  with  alkali.  From  one  of  these  fields  samples  of  soil  were 
taken  where  the  alkali  was  supposed  to  be  strongest  beneath  the  alfalfa, 
and  also  from  an  adjoining  untreated  alkali  spot,  which  was  said  to 
represent  conditions  before  alfalfa  was  planted.  The  results  are  given 
in  pounds  per  acre  in  four  feet  depth. 


Sulfate. 

Car- 
bonate. 

Common 
Salt. 

Total 
Alkali. 

Alkali  spot  before  alfalfa  was  planted. 
Alfalfa  field  ;  alkali  washed  down  .... 

60,120 
14,400 

720 

175,840 
1,040 

236,680 
18,640 

Here  the  surface  foot  of  the  natural  soil  contained  nearly  140,000 
pounds  of  common  salt,  a  prohibitory  amount.  Similar  experience  has 
been  had  near  Yuma,  Arizona. 

Difficulty  in  Draining  "  Black  "  Alkali  Lands. — An  import- 
ant exception  to  the  efficacy  of  draining,  however,  occurs  in 
the  case  of  black  alkali  in  most  lands.  In  this  case  either  the 
impervious  hardpan  or  (in  the  case  of  actual  alkali  spots)  the 

l  Bull.  133,  Cal.  Expt.  Sta..  by  R.  H.  Loughridge. 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     463 

impenetrability  of  the  surface  soil  itself  will  render  even  under- 
drains  ineffective  unless  the  salsoda  and  its  effects  on  the  soil 
are  first  destroyed  by  the  use  of  gypsum,  as  above  detailed. 
This  is  not  only  necessary  in  order  to  render  drainage  and 
leaching  possible,  but  is  also  advisable  in  order  to  prevent  the 
leaching-out  of  the  valuable  humus  and  soluble  phosphates, 
which  are  rendered  insoluble  (but  not  unavailable  to  plants) 
by  the  action  of  the  gypsum.  Wherever  black  alkali  is  found 
in  lands  not  very  sandy,  the  application  of  gypsum  should 
precede  any  other  efforts  toward  reclamation.  Trees  and 
vines  already  planted  may  be  temporarily  protected  from  the 
worst  effects  of  the  black  alkali  by  surrounding  the  trunks  with 
gypsum  or  with  earth  abundantly  mixed  with  it.  Seeds  may  be 
similarly  protected  in  sowing,  and  young  plants  in  planting. 

Stamping  of  Alkali  Lands. — It  should,  however,  be  remem- 
bered that  the  srvamping  of  alkali  lands,  whether  of  the  white 
or  black  kind,  is  fatal  not  only  to  their  present  productiveness, 
but  also,  on  account  of  the  strong  chemical  action  thus  induced, 
greatly  jeopardizes  their  future  usefulness.  Many  costly  in- 
vestments in  orchards  and  vineyards  have  thus  been  rendered 
unproductive,  or  have  even  become  a  total  loss. 

Reduction  of  Alkali  by  Cropping. — Another  method  for 
diminishing  the  amount  of  alkali  in  the  soil  is  the  cropping 
witli  plants  that  take  up  considerable  amounts  of  salts.  In 
taking  them  into  cultivation,  it  is  advisable  to  remove  en- 
tirely from  the  land  the  salt  growth  that  may  naturally  cover 
it,  notably  the  greasewoods  ( Sarcobatus.  Allcnrolfea),  with 
their  heavy  percentage  of  alkaline  ash  (  12  to  20  per  cent) 
Crop  plants  adapted  to  the  same  object  are  mentioned  farther 
on.  Such  crops  should  also,  of  course,  be  wholly  removed 
from  the  land. 

Total  Amounts  of  Salts  Compatible  TV///;  Ordinary  Crops: 
Tolerance  of  Culture  I'lants. — Since  the  amount  of  alkali  that 
reaches  the  surface  layer  is  largely  dependent  upon  the  varying 
conditions  of  rainfall  or  irrigation,  and  surface  evaporation,  it 
is  difficult  to  foresee  to  what  extent  that  accumulation  may  go, 
unless  we  know  the  total  amount  of  salts  present  tint  may  be 
called  into  action.  This,  as  already  explained,  can  ordinarily 
be  ascertained  by  the  examination  of  one  sample  representing 


SOILS. 

the  average  of  a  soil  column  of  four  feet.  By  calculating  the 
figures  so  obtained  to  an  acre  of  ground,  we  can  at  least  ap- 
proximate the  limits  within  or  beyond  which  crops  will  suc- 
ceed or  perish.  Applying  this  procedure  to  the  cases  repre- 
sented in  the  diagrams  (pp.  434,  452,  chapter  22)  and  estimat- 
ing the  weight  of  the  soil  per  acre-foot  at  4,000,000  pounds,  we 
find  in  the  land  on  which  barley  refused  to  grow  the  figures 
32,470  and  43,660  pounds  of  total  salts  per  acre,  respectively 
corresponding  to  0.203  per  cent,  for  the  first  figure  (the  second, 
representing  only  the  two  surface  feet,  is  not  strictly  compar- 
able). For  the  land  on  which  barley  gave  a  full  crop,  we  find 
for  the  May  sample  25, 550  pounds,  equivalent  to  0.159  per  cent, 
for  the  whole  soil  column  of  four  feet.  It  thus  appears  that  for 
barley  the  limits  of  tolerance  lie  between  the  above  two  figures. 
It  should  be  noted  that  in  this  case  a  full  crop  of  barley  was 
grown  even  when  the  alkali  consisted  of  fully  one-half  of  the 
noxious  carbonate  of  soda;  proving  that  it  is  not  necessary  in 
every  case  to  neutralize  the  entire  amount  of  that  salt  by  means 
of  gypsum,  which  in  the  present  case  would  have  required 
about  gl/2  tons  of  gypsum  per  acre — a  prohibitory  expenditure. 
Relative  Injuriousness  of  the  Several  Salts. — Of  the  three 
sodium  salts  that  usually  constitute  the  bulk  of  "  alkali,"  only 
the  carbonate  of  soda  is  susceptible  of  being  materially  changed 
by  any  agent  that  can  practically  be  applied  to  land.  So  far  as 
we  know,  the  salt  of  sodium  least  injurious  to  ordinary  vege- 
tation is  the  sulfate,  commonly  called  Glauber's  salt,  which 
ordinarily  forms  the  chief  ingredient  of  "  white  ''  alkali. 
Thus  barley  is  capable  of  resisting  about  five  times  more  of  the 
sulfate  than  of  the  carbonate,  and  quite  twice  as  much  as  of 
common  salt.  Since  the  maximum  percentage  that  can  be  re- 
sisted by  plants  varies  materially  with  the  kind  of  soil,  it  is 
difficult  to  give  exact  figures  save  with  respect  to  particular 
cases.  For  the  sandy  loam  of  the  Tulare  substation,  Cali- 
fornia, for  instance,  the  maximum  for  cereals  may  be  approxi- 
mately stated  to  be  one-tenth  of  i  per  cent,  for  salsoda :  a 
fourth  of  i  per  cent,  for  common  salt ;  and  from  forty-five  to 
fifty  one-hundred ths  of  one  per  cent  of  Glauber's  salt.  For  clay 
soils  the  tolerance  is  in  general  markedly  less,  especially  as  re- 
gards the  salsoda;  since  in  their  case  the  injurious  effect  on  the 


UTILIZATION   AND  RECLAMATION  OF  ALKALI  LANDS.     465 

tilling  qualities  of  the  soil,  already  referred  to,  is  superadded 
to  the  corrosive  action  of  that  salt  upon  the  plant. 

Effect  of  Differences  in  Composition  of  Alkali  Salts  on  Beets. — The 
marked  differences  which  may  occur  as  the  result  of  even  slight  variations 
in  the  proportions  of  the  several  salts  is  well  illustrated  in  the  subjoined 
diagram  of  observations  made  by  Dr.  G.  W.  Shaw,  of  the  Cal.  Expt. 
station,  upon  beet  fields  in  the  neighborhood  of  Oxnard,  Cal.  The 


<i.  73.— Alkali  curve  showing  percentage  of  Alkali  Salts  in  field  of  Sugar  Beets,  Uxnard,  Calif. 


Vic,.  74. — Heels  from  corresponding  positions  in  the  above  field. 

lands  lie   not   far  from   the  sea-shore,  and  saline  water  underruns  them 
for  considerable  distance  inland.      The  soil  and  subsoil  arc  quite  sandy, 
so   that    it   takes    irrigation    water   only  about  seven  hours  to  penetrate 
30 


466  SOILS. 

from  the  surface  to  bottom  water  at  seven  feet  depth.  The  land  on 
which  these  observations  were  made  are  apparently  level  to  the  eye, 
though  probably  the  alkali  belts  on  which  the  sugar  beets  were  "  poor  " 
are  slightly  depressed  swales. 

It  will  be  noted  that  here  the  beets  were  "  good  "  where  the 
sulfate  (Glauber's  salt)  ranged  up  to  .8%,  with  .10  to  .20  of 
common  salt ;  but  that  so  soon  as  the  latter  rose  above  .20,  the 
beets  were  poor  despite  the  low  percentage  of  Glauber's  salt; 
then  became  "  good  "  again  so  soon  as  the  common  salt  fell 
below  .20%,  although  the  Glauber's  salt  increased. 

TOLERANCE  OF  VARIOUS  CROP  PLANTS. 

The  following  table,  compiled  by  Dr.  R.  H.  Loughridge 
mainly  from  his  own  observations,1  gives  the  details  of  the 
tolerance  for  various  culture  plants  as  ascertained  at  the  several 
experiment  substations  in  California,  as  well  as  at  other  points 
in  that  State  and  in  Arizona  where  critical  cases  could  be 
found.  It  is  thought  preferable  to  investigate  analytically  such 
cases  in  the  field,  rather  than  to  attempt  to  obtain  results  from 
small-scale  experiments  artificially  arranged,  in  which  sources 
of  error  arising  from  evaporation  and  other  causes  are  most 
difficult  to  avoid. 

The  table  is  so  arranged  as  to  show  the  maximum  tolerance  thus  far 
observed  for  each  of  the  three  single  ingredients,  as  well  as  the  maximum 
of  total  salts  found  compatible  with  good  growth.  In  view  of  the  ex- 
tremely variable  proportions  between  the  three  chief  ingredients  found 
in  nature,  this  seems  to  be  the  only  manner  in  which  the  observations 
made  can  be  intelligibly  presented,  until  perhaps  a  great  number  of  such 
data  shall  enable  us  to  evolve  mathematical  formula?  expressing  the 
tolerance  for  the  possible  mixtures  for  each  plant.  For  it  is  certain 
that  the  tolerance-figures  will  be  quite  different  in  presence  of  other 
salts,  from  those  that  would  be  obtained  for  each  salt  separately ;  or  for 
the  calculated  mean  of  such  separate  determinations,  proportionally 
pro-rated.  It  must  also  be  remembered  that  in  all  alkali  soils,  lime 
carbonate  is  abundantly  present,  as  is,  nearly  always,  a  greater  or  less 
amount  of  the  sulfate  (gypsum).  As  already  stated,  according  to  the  in- 
vestigations of  Cameron  not  only  these  compounds,  but  also  calcium 
chlorid,  exert  a  protective  influence  against  the  injury  to  plant  growth 
from  compounds  of  sodium  and  potassium.  The  figures  here  given  can 
1  Bulletins  Nos.  128,  133  and  140,  Calif.  Expt.  .Station. 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.      467 

therefore  be  regarded  only  as  approximations,  subject  to  correction  by 
farther  observation.  They  are  arranged  from  the  highest  tolerances 
downward,  for  each  of  the  three  ingredients,  as  well  as  for  the  totals. 
The  latter  are  not,  of  course,  the  sums  of  the  figures  given  in  the  pre- 
ceding columns,  but  independent  data. 

HIGHEST    AMOUNT    OK   ALKALI    IN    WHICH    FRUIT   TREES    WKRE   FOUND 
UNAFFECTED.1 

Arranged  from  highest  to  lowest.     Pounds  per  acre  in  four  feet  depth. 


Sulfates 
(Glauber's  Salt). 


Cajbonate 

(Salsoda). 


Grapes 

Olives 

Figs 

Almonds 

Oranges 

Pears 

Apples 

Peaches 

Prunes 

Apricots 

Lemons 

Mulberry. . . . 


40.800  drapes. . . 
30,640  < (ranges. . 

24,4*0  Olives 

22.720  Pears. . . . 


Chlorid 

(Common   Salt). 


Total  Alkali. 


18,600  Almonds. 
1 7, Sew  Prunes.    . 

14,240  Kigs 

9,600  Peaches. . 


1,440 
1,360 

1,120 


0,240  Apples... 
8,640  Apricots.. 
4,480  Lemons. . 
3,360,  Mulberry. 


640 
4X0 

480 


Grapes 0.640  Grapes 45,7110 

Olives 6  640  Olives 40,160 

Oranges 3  360  Almonds 25, 560 

Almonds 2  400  l''igs 26,400 

Mulberry 2  240  Oranges 21,840 

Pears   i  3'«>  Pears 20.920 

Apples i  240  Apples 16,120 

Prunes i  200  Prunes 1 1,800 

Peaches i  ooo  Peaches 11,280 

Apricots 060  Apricots 10080 


Lemons 800  Lemons 

Kigs 800  Mulberry, 


5.760 
5.760 


OTHER    TREKS. 


Kiilreuteria  . . . .  51,040  Kolreuteria 9,920  Or.  Sycamore. ...   20.320  Kiilreuteria 73,600 

Kucal.  am 34,720  Or.   Sycamore 3,201  Kolreuteria 12,640  <  )r.  Sycamore 4?.7'-<> 

Or.  Sycamore.. .  19,240  I  >ate  Palm 2,800  Kucal.  am 2.960  Kucal.   am 40,400 

Wash.  Palm....  13.040  Kucal.  am 2,720  Camph.  Tree 1,420  Wash.  Palm 15,200 

Date  Palm 5.500  Wash.  Palm 1,200  Wash    Palm 1,040  I  >atc  Palm 8,328 

Camph.  Tree...  5,280  Camph.  Tree 320                                                 Camph.  Tree 7.020 


SMALL    (TI.TUkK.S. 


Saltbush  

125,640 

Saltbush  

Modiola  

.    40,860 

Saltbush  

.156.720 

Alfalfa,  old  ... 

102,4X0 

Barley  

•    12,17" 

Saltbush  

.      12,  ,20 

Alfalfa,  old.... 

.  110,320 

Alfalfa,  voung. 

1  1,120 

Bur  Clover  

.    1  1  300 

Sorghum  

9,6X0 

Alfalfa,  voung. 

15    1  '0 

Hairy  \  etch..  . 

63.720 

Sorghum  

.      9.840 

Celery  

..      9,'««> 

Sorghum  

.    81,710 

Sorghum  

6  ,,840 

Radish  

(  )nions  

Hairv  Vetch.  .  . 

(xj   -«»> 

Sugar  Beet  

52.640 

Modiola  

.      4.7"> 

Potatoes  

5810 

Radish  

.     l>2.*40 

Sunflower  

52.640 

Sugar  Beet  

.      4,000 

Sunflower  

•       5,44" 

Sunflower...    . 

.    59.x4a 

Radish  

51,880 

Gluten  Wheat.  .  . 

Sugar  Beet2.... 

.     10.240 

Sugar  Beet  

Artichoke  

38,720 

Artichoke  

Barley  

.       5.  "i" 

Modiola  

•     52,420 

Carrot  

24.880 

Lupin  

2   -2" 

Hairv  Vetch.... 

3   l<«> 

Artichoke  

.    4^.'i'o 

Gluten  Wheat.  . 

20.960 

Hairv  Vetch  

.      2.4*.. 

Lupin  

•      3-°4" 

Carrot  

Wheat  

'5,  '2ii 

Alfalfa  

2    t'O 

Carrot  

Barley  

25   >'o 

Barley  

12,020 

(  J  rashes  

2   \<  0 

Radish  

.      2.240 

Gluten  Wheat.. 

.  24,12.) 

Gnat  s  Rue  

I0,88o 

Kaffir  Corn  

I.Xoo 

Rve  

1.720 

Wheat    

Rve    

9,800 

Sweet   Corn.  .  .  . 

!.*.«' 

Artichoke  

.       1,4X0 

Bur   Clover.... 

I-.'OO 

Canaigre  

9,160 

Sunflower  

Gluten  Wheat.. 

Celery  

1   </'*0 

Rav  Grass  

6.920 

Wheat  

.        1  ,  1  *r> 

Wheat    

.       l,i'.o 

Rve  

.     12.4*0 

Modiola  

d  *o.> 

Carrot  

•        1.24" 

Grasses  

1,000 

Goat's  Rue  

Bur  Clover  .  .  . 

5.70" 

Rve  

White  Melilot.. 

440 

Lupin  

.       11.2-0 

5.44" 

('.oafs   Rue   .... 

Goat's  Rue  

Canaigre  

White  Melilot.. 

.     4.92° 

White  Melilot... 

4V" 

Canaigre  

Si 

Onions  

;*  1*0 

Celery  

4,080 

Canaigre  

12" 

Potatoes  

..   ;*.4*o 

Saltgrass  

44' 

Saitgrass  

.136.270 

Saltgrass  

.  70,360 

Saltgrass  

•  1^1  ,110 

1  The  several  columns  of  figures  are  independent  of  each  other;   the  "total" 
alkali  is  not  the  summation  for  the  three  salts  in  the  same  line. 

2  Figures  taken  from  Bulletin  169,  Calif.  Expt.  Station,  June,  1905. 


468  SOILS. 

Comments  on  the  Above  Table. — Considering  in  this  table, 
first,  the  plants  suitable  for  the  stronger  class  of  alkali  lands, 
it  may  be  said  generally  that  the  search  for  widely  acceptable 
kinds  has  not  been  very  successful.  It  is  true  that  cattle  will 
nibble  green  salt  grass  (Distichlis  spicata),  but  will  soon 
leave  it  for  any  dry  feed  that  may  be  within  reach.  The  enor- 
mous amount  of  salts  which  it  will  tolerate  in  the  soil  on 
which  it  grows,  and  the  doubtless  correspondingly  large 
amount  of  those  salts  which  it  will  absorb,  judging  from  its 
taste,  sufficiently  explain  the  reluctance  of  cattle  to  feed  on  it 
to  any  considerable  extent. 

The  same  is  true  of  all  the  fleshy  plants  that  grow  on  the 
stronger  alkali  lands,  and  are  knoxvn  under  the  general  desig- 
nation of  "  alkali  weeds."  When  stock  unaccustomed  to  it 
are  forced  by  hunger  to  feed  on  such  vegetation  to  any  con- 
siderable extent,  disordered  digestion  is  apt  to  result ;  which 
in  such  ranges,  however,  is  often  counteracted  by  feeding  on 
aromatic  or  astringent  antidotes,  such  as  the  gray  sagebrush 
and  the  more  or  less  resinous  herbage  of  plants  of  the  sun- 
flower family. 

In  the  Great  Basin  region,  lying  between  the  Sierra  Nevada 
and  the  front  range  of  the  Rocky  Mountains,  there  are,  aside 
from  the  grasses,  numerous  herbaceous  and  shrubby  plants 
that  afford  valuable  pasturage  for  stock,1  and  some  of  these 
grow  on  moderately  strong  alkali  land;  the  same  is  true  in 
California.  It  is  quite  possible  that  some  of  these  will  be  found 
to  lend  themselves  to  ready  propagation  for  culture  purposes 
as  well  as  they  do  for  restocking  the  ranges.  But  thus  far 
none  have  found  wider  acceptance,  probably  because  their  stiff 
branches  and  upright  habit  render  them  inconvenient  to  handle. 
It  will  require  more  extended  experience  and  experiment  be- 
fore any  of  these  will  be  definitely  adopted  for  propagation  by 
farmers  and  stockmen. 

1  See  Bulletin  No.  16  of  the  Wyoming  Experiment  Station;  also  Bulletin  Nos. 
2  and  12  of  the  Division  of  Agrostology,  and  Farmers' Bulletin  No.  108,  U.  S, 
Department  of  Agriculture. 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     469 

Saltbushes,  and  Herbaceous  Crops. 

Australian  Saltbushes. — Experience  in  California  indicates 
that  in  the  more  southerly  portion  of  the  arid  region,  un- 
palatable native  plants  may  be  largely  replaced,  even  on  the 
ranges,  by  one  or  more  species  of  the  Australian  saltbushes 
(Atriple.v  spp.},  long  ago  recommended  by  Baron  von  Mueller 
of  Melbourne;  of  which  one  (A.  seinibaccata)  has  proved  emi- 
nently adapted  to  the  climate  and  soil  of  California  and  is 
readily  eaten  by  all  kinds  of  stock.  The  facility  with  which  it 
is  propagated,  its  quick  development,  the  large  amount  of  feed 
yielded  on  a  given  area,  even  on  the  strongest  alkali  land  ordi- 
narily found,  and  its  thin,  flexible  stems,  permitting  it  to  be 
handled  very  much  like  alfalfa,  seem  to  commend  it  especially 
to  the  farmers'  consideration  wherever  better  forage  plants  can- 
not be  grown  and  the  climate  will  permit  of  its  use.  It  does 
not,  however,  resist  the  severe  cold  of  the  interior  plateau 
country,  and  is  wholly  out  of  place  in  the  Pacific  Coast  region 
where  summer  fogs  prevail.  Most  of  the  other  Australian 
species  have  an  upright,  shrubby  habit,  which  adapts  them  bet- 
ter to  browsing  than  to  pasture  proper.  The  same  is  true  of 
the  Argentine  species  (A.  Cachiyuynni'),  which  in  its  native 
pampas  is  highly  esteemed  for  that  purpose,  and  succeeds  well 
in  California.  Of  other  Australian  saltbushes,  A.  halimoidcs, 
I'csicarici  and  leptocarpa  are  the  most  promising;  the  latter  is 
somewhat  similar  in  habit  to  the  semibaccata,  but  is  not  as 
vigorous  a  grower.  Since  some  of  the  saltbushes  take  up 
nearly  one  fifth  of  their  dry  weight  of  ash  ingredients,1  largely 
common  salt,  the  complete  removal  from  the  land  of  a  five-ton 
crop  of  saltbush  hay  will  take  away  nearly  a  ton  of  the  alkali 
salts  per  acre.  This  will  in  the  course  of  some  years  be  quite 
sufficient  to  reduce  materially  the  saline  contents  of  the  land, 
and  will  frequently  render  possible  the  culture  of  ordinary 
crops. 

Modiola. — Alongside  of  the  saltbushes.   the   Chilean   plant 

1  Analyses  made  at  the  California  station  show  19.17  percent  of  ash  in  the  air- 
dry  matter  of  Australian  saltlnish.  (See  California  Station  IHilletin  Xo.  105; 
F.,  S.  R.,  vol.  6,  ]).  7iS).  Analyses  of  Russian  thistle  have  been  reported  showing 
over  20  per  cent  of  ash  in  dry  matter.  (See  Minnesota  Sta.  Bulletin  Xo.  34;  Iowa 
Sta.  Hull.  X'o.  26;  I-.  S.  K.,  vol.  6,  pp.  5S--553). 


470  SOILS. 

Modiola  procumbens,  now  generally  known  as  modiola  simply, 
deserves  attention, -as  it  makes  acceptable  pasture  where  alfalfa 
fails  to  make  a  stand  on  account  of  alkali.  It  is  a  trailing  plant 
with  medium-sized,  roundish  foliage,  and  roots  freely  at  the 
joints  where  they  touch  the  ground.  Unlike  the  saltbushes  it 
is  therefore  a  formidable  weed  where  it  is  not  wanted;  but  as 
according  to  California  experience  it  resists  as  much  as  52,000 
pounds  of  salts  per  acre,  even  when  41,000  of  these  is  common 
salt,  it  is  likely  to  be  useful  in  many  cases,  particularly  as  an 
admixture  to  a  saltbush  diet  for  stock,  as  it  does  not  absorb 
as  much  salt  as  the  latter.  It  seems  best  adapted  to  pasturage. 

As  the  table  shows  that,  once  grown  to  the  age  of  a  few 
years,  alfalfa  will  resist  a  percentage  of  alkali  next  to  the  salt- 
bush,  it  will  generally  be  worth  while,  in  lands  otherwise 
adapted  to  alfalfa,  to  prepare  the  land  by  leaching-down  (see 
above)  so  as  to  secure  a  stand  of  the  more  valuable  crop. 

Native  Grasses.1 — Of  all  known  plants  that  stock  will  eat 
somewhat  freely,  the  tussock  grass  (Sporobolus  airoidcs,  of 
which  a  figure  is  given  farther  on),  a  native  of  the  southern 
arid  region,  endures  the  largest  amounts  of  alkali ;  having  been 
found  growing  well  on  land  containing  the  enormous  amount 
of  nearly  half  a  million  pounds  of  salts  per  acre,  although  it 
will  thrive  with  only  49,000  pounds  in  the  soil.  What  it  will 
do  under  cultivation  has  never  been  fairly  tested;  but  its  bare 
tussocks,  killed  by  the  excessive  browsing  of  stock,  testify  to 
its  acceptableness  as  forage.  It  does  not  seem  to  absorb  ex- 
cessive amounts  of  salts. 

Aside  from  the  alkali  grass  proper  (Distichlis),  mentioned 
above,  the  so-called  rye  grass  of  the  Northwest  (Elymus  con- 
densatus)  is  probably,  next  to  the  tussock  grass,  the  most  re- 
sistant species  among  the  wild  grasses.  Its  southern  form, 
with  several  others  not  positively  identified,  occupies  largely 
the  milder  alkali  lands  of  southern  California.  This  grass, 
though  rather  coarse,  is  regularly  cut  for  hay  in  the  low 
grounds  of  Oregon  and  Washington. 

1  It  should  be  understood  that  the  plants  so  referred  to  are  exclusively  the  trut 
grasses,  recognized  as  such  by  every  child,  and  not  forage  plants  generally;  which 
are  sometimes  so  designated  ;  not  only  by  farmers,  but  by  some  authors  who  fail 
to  appreciate  the  practical  importance  of  the  distinction,  which  makes  it  necessary 
that  farmers  should  be  taught  to  understand  it. 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS. 


471 


Doubtless  some  of  the  indigenous  grasses  of  the  interior 
plateau  region  and  of  the  great  plains  east  of  the  Rocky  Moun- 
tains, such  as  the  buffalo  and  grama  grasses,  as  well  as  several 
of  the  wheat  grasses  (Agropyron)  and  bunch  grasses  (Fes- 
tuca,  Poa,  Stif>a,  etc.)  will  prove  resistant  to  larger  propor- 
tions of  alkali  than  the  meadow  and  pasture  grasses  of  the 
regions  of  summer  rains. 

Cultivated  Grasses. — The  superficial  rooting  and  fine 
fibrous  roots  of  the  true  annual  grasses  render  them,  as  a 
whole,  rather  sensitive  to  alkali ;  yet  the  cereals — barley,  wheat, 
rye  and  oats — resist,  as  the  table  shows,  the  average  alkali 
salts  to  the  extent  of  from  17,000  total  salts,  with  not  exceed- 
ing 1500  pounds  of  carbonate,  in  the  case  of  the  more  delicate 
varieties  of  wheat,  to  over  25,000  pounds  per  acre  in  the  case 
of  barley,  which  with  the  gluten  wheats  and  rye  seems  to  have 
the  highest  tolerance-figure.  The  special  adaptation  of  gluten 
wheats  to  arid  conditions  is  thus  emphasized.  The  roots  of 
these  cereals  are  comparatively  stout,  with  thick  epidermis. 

Among  the  cultivated  forage  grasses  proper,  the  Australian 
variety  of  the  English  ray  (generally  miscalled  rye)  grass 
seems  most  resistant.  The  eastern  fescues.  Kentucky  blue 
grass,  and  others  at  home  in  the  humid  region  are  easily  in- 
jured, as  those  who  try  to  maintain  lawns  on  alkali-tainted 
lands,  or  by  irrigation  with  alkali  waters,  know  to  their  sorrow. 
To  these  grasses  common  salt  and  bittern  (  magnesium  chlorid) 
seem  to  be  particularly  injurious,  and  they  tolerate  but  little 
"  black  alkali." 

On  the  rather  close-textured  soil  at  Chino.  Cali fornia.  the 
loliums.  including  the  darnel  ("California  cheat"),  and  the 
Australian  and  Italian  ray  ("rye")  grasses,  succeed  fairly  on 
land  containing  as  much  as  6.000  pounds  of  (white)  salts. 
Most  other  cultivated  grasses  failed  conspicuously  alongside 
of  these.  It  must  be  remembered  that  in  more  loose-textured, 
sandy  lands  than  those  in  which  these  tests  were  made,  the 
above  figures  for  tolerance  would  probably  be  increased  by  30 
percent  or  more. 

Maize  is  rather  sensitive  to  alkali,  and  suffers  even  on 
slightly  alkaline  land,  owing  doubtless  to  the  large  develop- 
ment of  fine  white  rootlets  near  the  surface,  so  familiar  t<> 
corn-growers.  The  Sorgliuins,  and  especially  Egyptian  corn 


472  SOILS. 

(durra)  are  much  less  sensitive,  as  the  table  shows,  and  are 
among  the  first  crops  to  be  tried  on  alkali  lands.  The  related 
millets  share  this  resistance  more  or  less,  and  we  often  see  on 
cultivated  lands  in  the  alkali  region  fine  stands  of  barnyard 
grass  (Panicum  crusgalli)  of  which  the  variety  (  ?)  P.  muti- 
cum  is  said  by  observers  of  the  U.  S.  Dept.  of  Agriculture  to 
be  specially  resistant,  and  acceptable  to  stock.  One  of  the  most 
successful  grasses  on  the  light  alkali  lands  near  Chino,  wyhere 
most  of  the  commonly  cultivated  grasses  fail,  was  a  near 
relative  of  the  barnyard  grass,  the  Eleusinc  coracana,  which 
produces  heavy  crops  of  a  millet-like  grain  much  relished  by 
poultry,  and  also  by  stock.  This  grass,  largely  grown  in 
Egypt,  has  succeeded  well  all  over  the  ground  whose  alkali 
content  ranges  up  to  12,000  pounds  per  acre,  but  failed  where 
the  salts  reached  38,840  pounds  in  the  surface  foot.  Next  to 
this,  in  point  of  success,  were  the  pearl  millet  (Pennisctum 
typhoideum)  and  teosinte,  Hungarian  brome  grass,  and  Japan- 
ese millet,  on  land  containing  about  9,000  pounds  of  (chiefly 
"  white  ")  salts  per  acre. 

Other  Herbaceous  Crops.  Legumes. — Both  the  natural 
growth  of  alkali  lands  and  experimental  tests  seem  to  show 
that  this  entire  family  (peas,  beans,  clovers,  etc.)  are  among 
the  more  sensitive  and  least  available  wherever  black  alkali 
exists;  while  fairly  tolerant  of  the  white  (neutral)  salts.  Ap- 
parently a  very  little  salsoda  suffices  to  destroy  the  tubercle- 
forming  organisms  that  are  so  important  a  medium  of  nitro- 
gen-nutrition in  these  plants.  Excepting  the  melilots,  alfalfa 
with  its  hard,  stout  and  long  taproot,  seems  to  resist  best  of  all 
these  plants. 

As  a  general  thing,  taprooted  plants,  when  once  established,  resist 
best,  for  the  obvious  reason  that  the  main  mass  of  their  feeding  roots 
reaches  below  the  danger  level.  Another  favoring  condition,  already 
alluded  to,  is  heavy  foliage  and  consequent  shading  of  the  ground ; 
alfalfa  happens  to  combine  both  of  these  advantages.  There  has  been 
some  difficulty  in  obtaining  a  full  stand  of  alfalfa  in  the.portion  of  the 
Chino  substation  tract  containing  from  4000  to  6000  pounds  of  (largely 
black)  alkali  salts  per  acre  ;  but  once  obtained,  it  has  done  very  well. 

The  only  other  plant  of  this  family  that  succeeds  well  on 
this  land,  and  even  (at  Tulare)  on  soil  considerably  stronger 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     473 

(probably  between  20,000  and  30,000  pounds)  are  the  two 
melilots,  M.  indica,  and  alba;  the  latter  (the  Bokhara  clover) 
is  a  forage  plant  of  no  mean  value  in  moist  climates,  but  some- 
what restricted  in  its  use  in  the  arid  region  because  of  the 
very  high  aroma  it  develops,  especially  in  alkali  lands ;  so  that 
stock  will  eat  only  limited  amounts,  best  when  intermixed 
with  other  forage,  such  as  the  saltbushes.  The  yellow  melilot 
is  highly  recommended  by  the  Arizona  Experiment  Station  as 
a  green-manure  plant  for  winter  growth ;  but  farther  north  it 
is  a  summer-growing  plant  only,  and  is  refused  by  stock.  As 
already  stated,  very  few  plants  belonging  to  this  family  are 
naturally  found  on  alkali  lands,  and  attempts  to  grow  them, 
even  where  only  Glauber's  salt  is  present,  have  been  but  very 
moderately  successful. 

For  most  of  the  legumes  the  limit  of  full  success  seems  to 
lie  between  3000  and  4000  pounds  to  the  acre.  A  marked  ex- 
ception, however,  occurs  in  the  case  of  the  hairy  vetch,  as 
shown  in  the  table,  where  it  is  credited,  on  the  basis  of  re- 
peated experiments,  with  a  tolerance  of  nearly  70.000  pounds. 
This  amount  was  attained,  however,  in  rather  sandy  soils. 
Probably  some  of  the  Algerian  vetches  will  likewise  prove 
more  resistant  than  those  which  are  natives  of  humid  climates. 

Mustard  l'ainil\. — As  in  the  case  of  the  legumes,  wild  plants 
of  the  mustard  family  are  rare  on  alkali  lands;  and  correspond- 
ingly, the  cultivated  mustard,  kale.  rape,  etc.,  fail  even  on  land 
quite  weak  in  alkali.  Their  limit  of  tolerance  seems  to  lie  near 
4.000  to  5,000  pounds  ]>er  acre  even  of  white  salts.  Hence 
turnips  and  radishes  do  not  flourish  on  alkali  lands. 

Sunflir^'cr  I:uinity. — Several  of  the  hardiest  of  the  native 
''alkali  weeds"  belong  to  the  sunflower  family,  and  the  com- 
mon wild  sunflowers  (  Hclianthus  calif ornicus  and  //.  animus] 
are  common  on  lands  pretty  strongly  alkaline.  The  cultivated 
Russian  sunflower,  as  the  table  shows,  resists  the  effects  of 
nearly  60,000  pounds  of  total  alkali,  of  which  52.640  pounds 
was  sulfate  ((ilauber's  salt),  and  5440  common  salt.  This,  it 
will  be  seen,  is  a  very  high  tolerance,  so  that  this  sunflower, 
yielding  such  excellent  poultry  feed,  is  very  widely  available 
Correspondingly,  the  "  Jerusalem  artichoke."  itself  a  sun- 
flower, is  among  the  available  crops  on  moderately  strong 
alkali  soils:  and  so.  doubtless,  are  other  members  of  the  same 


474 


SOILS. 


relationship  not  yet  tested,  such  as  the  true  artichoke,  salsify, 
etc.  Chicory,  belonging  to  the  same  family,  yielded  roots  at 
the  rate  of  twelve  tons  per  acre,  on  land  of  the  Chino  tract 
containing  about  8,000  pounds  of  salts  per  acre. 

Root  Crops. — It  seems  to  be  generally  true  that  root  crops 
suffer  in  quality,  however  satisfactory  may  be  the  quantity, 
harvested  on  lands  rich  in  salts,  and  especially  in  chlorids 
(common  salt).  It  was  noted  at  the  Tulare  substation  (Cali- 
fornia) that  the  tubers  of  the  artichoke  were  inclined  to  be 
"  squashy  "  in  the  stronger  alkali  land,  and  failed  to  keep  well ; 
the  same  was  true  of  potatoes,  which  were  very  watery;  and 
also  of  turnips  and  carrots.  It  is  a  fact  well  known  in  Europe, 
that  potatoes  manured  with  kainit  (chlorids  of  potassium  and 
sodium)  are  unfit  for  the  manufacture  of  starch,  and  are  gen- 
erally of  inferior  quality.  But  this  is  found  not  to  be  the  case 
when,  instead  of  the  chlorids,  the  sulfate  is  used ;  hence  the  ad- 
vice, often  repeated  by  the  California  station,  that  farmers  de- 
siring to  use  potash  fertilizers  should  call  for  the  "  high-grade 
sulfate  "  instead  of  the  cheaper  kainit,  which  adds  to  the  in- 
jurious salts  already  so  commonly  present  in  lowland  soils  of 
the  arid  region.  Such  root  crops  are,  however,  available  for 
stock  feed. 

The  common  beet  (including  the  mangel-wurzel)  is  known 
to  succeed  well  on  saline  seashore  lands,  and  it  maintains  its 
reputation  on  alkali  lands  also.  Being  especially  tolerant  of 
common  salt,  it  may  be  grown  where  other  crops  fail  on  this 
account ;  but  the  roots  so  grown  are  strongly  charged  with 
common  salt,  and  have,  as  is  well  known,  been  used  for  the 
purpose  of  removing  excess  of  the  same  from  seacoast-marsh 
lands.  Such  roots  are  wholly  unfit  for  sugar-making. 

It  is  quite  otherwise  with  Glauber's  salt  (sodium  sulfate)  ; 
and  as  this  is  very  commonly  predominant  in  alkali  lands, 
either  before  or  after  the  gypsum  treatment,  this  fact  is  of 
great  importance,  for  it  frequently  permits  of  the  successful 
growing  of  the  sugar  beet ;  as  has  been  abundantly  proved  at 
the  Chino  ranch,  where  land  containing  as  much  as  60,000 
pounds  of  salts,  mostly  this  compound,  has  yielded  roots  of 
very  high  grade,  both  as  to  sugar  percentage  and  purity.  But 
the  analyses  of  the  Oxnard  soil  show  that  more  than  10,000 


UTILIZATION   AND  RECLAMATION  OF  ALKALI  LANDS. 


475 


pounds  of  common  salt  will  be  required  to  render  sugar  beets 
unsatisfactory  for  sugar-making. 

Passing  to  stem  crops,  we  find  that  asparagus,  originally 
itself  a  denizen  of  the  sea-board,  resists  considerable  amounts 
(not  yet  exactly  determined)  of  common  salt  as  well  as  of 
Glauber's  salt.  It  is  even  claimed  that  when  grown  with  a 
dressing  of  common  salt  the  asparagus  is  more  tender  and 
savory.  But  it  is  quite  sensitive  to  "  black  alkali,"  which  must 
be  neutralized  with  gypsum  to  render  it  harmless. 

Celery  did  well  with  13.640  pounds,  of  which  nearly  10,000 
was  common  salt.  But  with  30,000  pounds  the  plants  were 
killed. 

Rhubarb  was  a  conspicuous  failure,  even  in  the  weak  and 
mostly  "  white  "  alkali  lands  of  the  Chino  station  tract. 

Textile  Plants. — Japanese  lieinp,  while  young,  seemed  to 
have  a  hard  struggle  with  the  alkali,  but  at  the  end  of  the  sea- 
son stood  eight  feet  high.  The  ramie  plant,  also,  will  bear 
moderately  strong  alkali,  apparently  somewhat  over  12,000 
pounds  per  acre,  ria.r  has  not  been  tested  in  cultivation;  but 
the  wide  distribution  of  wild  tlax  all  over  the  arid  portions  of 
the  States  of  Oregon  and  Washington,  would  seem  to  indicate 
that  it  is  not  very  sensitive.  .Another  textile  plant,  the  Indian 
mallow  (slbutilon  ar'icennae},  was  found  to  fail  on  the  Chino 
alkali  soil.  But  its  close  relative,  cotton,  does  not  seem  to  be 
specially  sensitive,  according  to  the  experience  had  with  it  in 
the  Merced  river  bottom  in  California  ;  and  its  culture  is  exten- 
sive in  Kgypt,  where  no  particular  care  seems  to  be  exercised  in 
selecting  the  land  for  the  crop.  It  is  just  possible  that  the 
saline  content  of  the  soil  Ins  in  California,  as  well  as  in  the 
Atlantic  sea-islands,  contributed  to  the  superior  length  of  the 
liber  shown  in  the  measurements  made  during  the  Census  work 
of  iScSo.1 

Ti'lerance  of  Shrubs  and  Trees. 

GrapC"'incs. — The  European  grape.  }'itis  I'inifera,  is  quite 
tolerant  of  white  or  neutral  alkali  salts,  and  will  resist  even  a 
moderate  amount  of  the  black  so  long  as  no  hardpan  is  allowed 
to  form.  At  the  Tulare  substation  it  was  found  that  grape- 

1  Report  on  Cotton  Culture;  loth  Census  of  the  United  States,  vol.  ^,  pp.  23 
to  34. 


4;6  SOILS. 

vines  did  well  in  sandy  land  containing  35,230  pounds  of  alkali 
salts,  of  which  one  half  was  Glauber's  salt,  9,640  pounds  cor- 
bonate  of  soda,  7,550  pounds  of  common  salt,  and  750  pounds 
nitrate  of  soda.  They  were  badly  distressed  where,  of  a  total 
of  37,020  pounds  of  alkali  salts,  25,620  pounds  was  carbonate 
of  soda ;  while  where  the  vines  had  died  out,  there  was  found  a 
total  of  73,930  pounds,  with  37,280  pounds  of  carbonate.  The 
European  vine,  then,  is  considerably  more  resistant  of  alkali 
even  in  its  worst  (black)  form,  than  barley  and  rye,  at  least 
on  sandy  land ;  and  it  seems  likely  that  the  native  grapevines  of 
the  Pacific  coast,  calif ornica,  and  arisonica,  would  resist  even 
better ;  a  point  still  under  experiment. 

Experience,  however,  has  shown  that  vines  rapidly  succumb 
when  by  excessive  irrigation  the  bottom  water  is  allowed  to 
rise,  increasing  the  amount  of  alkali  salts  near  the  surface,  and 
shallowing  the  soil  at  their  disposal.  Such  over-irrigation  has 
been  a  fruitful  cause  of  injury  to  vineyards  in  the  Fresno  re- 
gion, and  would  doubtless  if  practiced  kill  most  of  the  vines  at 
the  Tulare  substation,  which  are  now  flourishing.  In  such 
cases,  sometimes  the  formation  of  hardpan  is  followed  by  that 
of  a  concentrated  alkaline  solution  above  it,  strong  enough  to 
corrode  the  roots  themselves,  and  not  only  killing  the  vines, 
but  rendering  the  land  unfit  for  any  agricultural  use  whatso- 
ever. The  swamping  of  alkali  lands,  whether  of  the  white  or 
black  kind,  is  not  only  fatal  to  their  present  productiveness, 
but,  on  account  of  the  strong  chemical  action  thus  induced, 
greatly  jeopardizes  their  future  usefulness.  Many  costly  in- 
vestments in  orchards  and  vineyards  have  thus  been  rendered 
unproductive,  or  have  even  become  a  total  loss. 

It  should  be  remembered  in  this  connection  that  as  the  roots 
of  vines  will,  when  unobstructed,  go  to  depths  of  fifteen  and 
even  twenty  feet,  a  subsequent  rise  of  the  bottom  water  from 
leaky  irrigation  ditches  will  drown  out  the  ends  of  the  deep 
roots  and  thus  cause  the  whole  root  system  to  become  diseased, 
inevitably  resulting  in  unproductiveness,  if  not  death,  of  the 
vine. 

Citrus  Trees. — Although  the  high  figure  of  nearly  27,000 
pounds  for  the  tolerance  of  citrus  trees,  as  given  in  the  table, 
seems  to  place  them  rather  high  on  the  list,  such  high  tolerance 
actually  occurs  only  in  very  sandy  soils,  and  when  common 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     477 

salt  is  in  small  proportion.  Generally  speaking,  the  citrus 
tribe  are  rather  sensitive  to  alkali  salts,  and  more  especially  to 
common  salt.  In  fact,  as  to  the  high  tolerance-figure  given  in 
the  table,  observed  in  sandy  land,  the  alkali  there  contained 
only  a  trace  of  common  salt.  Young  seedling  trees  are  par- 
ticularly sensitive ;  so  that  it  is  often  difficult  to  obtain  a  stand 
even  when,  later  on,  the  feeding  roots  descend  beyond  the 
reach  of  injury.  In  the  close-textured  lands  of  Chino,  young 
trees  hardly  maintained  life  with  more  than  5.000  pounds  of 
total  salts.  Near  Riverside,  full-grown  trees  perished  under 
the  influence  of  bottom  water  containing  0.2$%,  or  146  grains 
of  salt  per  gallon,  which  impregnated  the  ground;  correspond- 
ing to  about  9,000  pounds  per  acre  in  four  feet. 

In  the  sandy  loam  lands  near  Corona,  trees  eighth-ears  old 
suffered  severely  when  by  irrigation  with  alkali-water  the 
alkali-content  of  the  land  reached  11,000  pounds  per  acre;  as 
illustrated  in  Figs.  Nos.  44,  and  45.  At  another  point  in 
the  same  region,  two  representative  trees  were  selected  for 
comparison,  five  rows  apart  on  land  absolutely  identical ;  one 
of  these  retained  its  leaves,  though  suffering,  the  other  was 
completely  leafless.  The  leaching  of  the  alkali  to  the  depth  of 
four  feet  gave  the  following  results,  calculated  to  pounds  per 
acre: 

Sulfates.          Carbonates.  Chlorids.  Total. 

Poor  tree 4.720  i6So  2,520  8,920 

Better  tree. ..     4,120  2,360  720  7,-OO 

Here  it  is  apparently  the  excess  of  common  salt  to  which  the 
difference  is  due.  and  this  despite  the  higher  content  of  carbon- 
ate of  soda  in  the  soil  bearing  the  better  tree. 

On  the  other  hand,  at  the  Tulare  substation  orange  trees 
(sour  stock)  maintain  vigorous  growth  and  good  bearing  in  a 
very  sandy  tract  which  to  the  depth  of  seven  feet  showed  an 
aggregate  content  of  26,840  pounds  of  salts  (or  22.780  to 
four  feet  depth)  ;  but  which  is  never  irrigated.  (  See  diagram 
Xo.  66).  The  salts  in  this  case  consists  wholly  of  sulfate  and 
carbonate  of  soda  in  the  ratio  of  fifty- four  to  forty-two,  im- 
plying the  presence  of  nearly  12,000  pounds  of  salsoda  within 
reach  of  the  tree  roots;  yet  in  the  absence  of  common  salt,  no 
perceptible  injury  or  even  stress  upon  the  trees  has  been  noted. 

According  to  observations  made  in  San  Diego  county.  Calif., 


478  SOILS. 

lemqn  trees  are  even  more  sensitive  to  common  salt  than 
oranges,  since  a  total  content  of  8,000  pounds  per  acre,  about 
one-third  of  which  was  common  salt,  seemed  to  render  the 
trees  wholly  unprofitable. 

In  view  of  these  facts,  showing  that  common  salt  is  the  por- 
tion of  alkali  by  far  most  injurious  to  citrus  trees,  great  care 
should  be  taken  in  the  use  of  irrigation  waters  to  exclude  those 
charged  with  that  compound ;  and  also  to  avoid  locating  citrus 
orchards  on  land  already  impregnated  with  common  salt. 

The  olive  tree,  as  the  table  shows,  is  among  the  most  re- 
sistant to  alkali  salts,  approaching  the  grape  in  this  respect. 
This  might  have  been  anticipated  from  its  extended  culture  in 
the  arid  regions  of  the  old  world,  including  Palestine  and 
northern  Africa,  where  alkali  lands  abound.  It  is  probable 
that  the  figure  given  in  the  table  does  not  yet  show  the  extreme 
limit  of  its  endurance. 

California  experience  with  the  date  palm,  as  the  table  shows, 
credits  it  with  an  endurance  not  exceeding  8320  pounds  of 
total  salts.  This  is  doubtless  an  underestimate,  for  in  the 
Sahara  desert  and  Egypt  it  is  credited  with  being  the  culture 
which  will  succeed  in  stronger  alkali  than  any  other  cultural 
plant ;  and,  according  to  Mr.  Means  of  the  United  States  De- 
partment of  Agriculture,  it  is  sometimes  irrigated  with  water 
containing  as  much  as  200  grains  of  salts  per  gallon.  It  should 
be  remembered,  however,  that  these  trees  always  grow  in  very 
sandy  lands ;  and  in  the  desert  regions  it  is  often  grown  below 
the  surface  of  the  ground,  so  as  to  render  it  wholly  independ- 
ent of  the  alkali  accumulations  on  the  surface.  The  extreme 
limit  of  its  endurance  must  therefore  remain  in  doubt  until 
more  extended  experiments  have  made  more  definite  data 
available. 

Deciduous  OrcJiard  Trees. 

Among  deciduous  orchard  trees,  strangely  enough,  the 
almond  stands  alongside  of  the  fig  in  alkali-resistance,  as  indi- 
cated in  the  table.  The  pcacJi  seems  to  be  much  more  sensitive, 
ranking  near  the  apricot  and  prune,  whose  tolerance  is  less 
than  half  as  high.  That  the  pear  and  apple,  generally  counted 
among  the  more  northern  fruits  in  the  humid  region,  should 
excel  these  stone  fruits  in  endurance  of  alkali,  is  rather  unex- 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS. 


479 


pected ;  and  the  figures  concerning"  the  whole  group  of  these 
rosaceous  fruits  admonish  us  that  it  is  unsafe  to  predict,  with- 
out trial,  what  may  he  the  outcome  of  culture  tests.  Thus 
plum  trees,  apparently  in  good  condition,  sometimes  suddenly 
begin  to  fail  when  starting  to  bear ;  the  fruit  appears  normal 
on  the  outside  for  a  time,  but  the  pit  fails  to  form,  being  at 
times  flattened  out  like  a  piece  of  pasteboard ;  and  the  fruit 
does  not  mature.  Yet  there  is  no  observable  injury  to  the  base 
of  the  trunk,  or  to  the  roots.  On  the  other  hand,  pears  do  well 
even  when  the  outside  bark  around  the  root-crown  is  black- 
ened by  the  action  of  the  alkali  salts.  But  38.000  pounds,  even 
of  sulfate,  proves  too  much  for  the  pear. 

The  quince  appears  to  be  materially  more  resistant  than  the 
apple  or  pear.  It  probably  ranges  alongside  of  the  fig,  the  soil- 
adaptations  of  which  it  shares  in  other  respects  also. 

The  English  i^alnnt  resents  even  a  slight  taint  of  black 
alkali;  but  is  fairly  tolerant  of  "  white"  salts,  as  is  shown  in 
the  peculiarly  suitable  light  loam  soils  on  the  lower  Santa  Clara 
river,  in  Ventura  county,  as  well  as  in  Orange  county.  Cali- 
fornia. 

Close  figures  for  the  limits  of  alkali  tolerance  in  the  case  of 
deciduous  orchard  trees  cannot  easily  be  given  or  determined, 
owing  to  the  difficulties  inherent  in  the  differences  of  root  pene- 
tration in  the  several  soils  and  localities;  as  well  as  the  fact 
already  alluded  to,  that  in  close-textured  soils  the  tolerance  is 
in  general  decidedly  less  than  in  sandy  lands.  1  lence  the 
figures  in  the  table  must  be  taken  as  more  nearlv  represent- 
ing relative  tolerances,  rather  than  absolute  data  to  be  ap- 
plied in  every  case.  As  regards  the  stone  fruits,  it  should 
be  remembered  that  the  Myrobalan  root,  being  at  home  in 
Asia  Minor,  where  alkali  abounds,  should  when  practicable  be 
used  wherever  alkali  conditions  exist,  in  preference  to  all  but 
the  almond,  which  seems  to  resist  well,  even  on  its  own  root, 
but  has  not  as  wide  a  range  of  adaptations  as  a  grafting  stock- 
as  the  myrolnlan.  While  most  of  the  other  stone  fruits  at  the 
Tulare  substation  were  on  myrabalan  roots,  the  stock  of  those 
in  outside  orchards  was  mostly  in  doubt.  It  is  also  to  be  kept 
in  mind  that  different  varieties  of  the  same  fruit — c.  g..  pears 
and  apples — show  a  not  inconsiderable  variation  in  their  resist- 
ance. 


480  SOILS. 

Timber  and  Shade  Trees. 

Of  trees,  forest  and  shade,  suitable  for  alkali  lands,  some 
native  ones  call  for  mention.  One  is  the  California  white  or 
valley  oak  (Quercus  lobata),  which  forms  a  dense  forest  of 
large  trees  on  the  (almost  throughout  somewhat  alkaline) 
delta  lands  of  the  Kaweah  River  in  California,  and  is  found 
scatteringly  all  over  the  San  Joaquin  Valley.  Unfortunately 
this  tree  does  not  supply  timber  valuable  for  aught  but  fire- 
wood or  fence  posts,  being  quite  brittle. 

The  native  cottonwoods,  while  somewhat  retarded  and 
dwarfed  in  their  growth  in  strong  alkali,  are  quite  tolerant  of 
the  white  salts,  especially  of  Glauber's  salt.  As  they  usually 
grow,  near  to  the  water,  their  tolerance  for  alkali  salts  is  diffi- 
cult to  ascertain. 

Of  other  trees,  the  oriental  plane,  or  sycamore,  and  the  black 
locust  have  proved  the  most  resistant  in  the  alkali  lands  of  the 
San  Joaquin  Valley ;  and  the  former  being  a  very  desirable 
shade  tree,  it  should  be  widely  used  throughout  the  regions 
where  alkali  prevails  more  or  less.  The  ailantus  is  about 
equally  resistant,  and  but  for  the  evil  odor  of  its  flowers,  de- 
serves strong  commendation. 

Of  the  eucalypts,  the  narrow-leaved  Eucalyptus  amygdalina 
(one  of  the  "red  gums")  and  the  closely  related  viminalis, 
seem  to  be  least  sensitive,  and  in  some  cases  have  grown  in 
alkali  lands  as  rapidly  as  anywhere.  The  rostrata,  as  well  as 
the  pink  flowered  variety  of  sideroxylon,  are  now  doing  about 
as  well  as  the  amygdalina  at  Tulare,  where  at  first  they  seemed 
to  suffer.  The  common  blue  gum,  globulus,  is  much  more 
sensitive. 

Of  the  Acacias,  the  tall-growing  A.  melanoxylon  ("black 
acacia  ")  resists  pretty  strong  alkali,  even  on  stiff  soil;  as  can 
be  seen  at  Tulare  and  Bakersfiekl,.  California,  where  there  are 
trees  nearly  two  feet  in  diameter.  The  beautiful  A.  lophantha 
(Albiczia)  has  in  plantings  made  along  the  San  Joaquin  Valley 
railroad  shown  considerable  resistance,  likewise;  but  it  is  quite 
sensitive  to  frost. 

Of  other  Australian  trees,  one  of  the  Australian  "  pines," 
(Casuarina  cquisetifolia},  is  doing  well  on  fairly  strong  alkali 
land  in  the  San  Joaquin  Valley. 


UTILIZATION   AND  RECLAMATION  OF  ALKALI  LANDS.      481 

A  remarkably  alkali-resistant  shrub  or  small  tree  is  the 
pretty  Kcclrcuteria  paniculata  from  China,  which  at  Tulare  is 
growing  in  some  of  the  strongest  alkali  soil  of  the  tract.  Un- 
fortunately it  is  available  mainly  for  ornamental  purposes;  its 
wood,  while  small,  is  very  hard  and  makes  excellent  fuel. 

Of  trees  indigenous  to  the  Atlantic  and  East  Central  United 
States,  the  Tulip  tree,  the  Linden,  and  most  other  trees  of  the 
humid  region,  including  the  English  oak  ( Qucrcus  pcdun- 
culata)  become  stunted  in  alkali  soils.  The  honey  locust,  being 
particularly  adapted  to  calcareous  lands,  does  moderately  well 
on  alkali  lands,  but  its  thorns  and  imperfect  shade  render  it 
not  very  desirable.  The  black  locust  and  the  dins  have  on  the 
whole  done  best.  The  eastern  maples  are  not  successful;  but 
the  California  maple  (Acer  macrophylluin}  and  the  box  elder 
(Ncgundo  californica)  have  done  fairly  well  in  the  lighter 
alkali  lands  of  the  San  Joaquin  Valley. 

The  Conifers — Pines,  firs,  cedars,  cypress,  etc.,  are  very 
sensitive  to  black  alkali  and  will  not  endure  much  even  of  the 
4"  white  "  salts.  Even  the  native  juniper  of  the  mesas  carefully 
adheres  to  the  portions — breaks  and  upper  slopes,  hilltops,  etc. 
• — which  are  more  or  less  leached  by  the  scanty  rains  of  these 
regions. 

INDUCEMENTS  TOWARD  THE  RECLAMATION   OF  ALKALI   LANDS. 

The  expense  involved  in  the  reclamation  of  strong  alkali 
lands  naturally  gives  rise  to  the  question  whether  adequate 
advantages  are  likely  to  be  derived  from  such  expenditure; 
specially  when  the  last  resort — underdraining  and  leaching — 
has  to  be  adopted. 

Those  familiar  with  the  alkali  regions  are  aware  how  often 
the  occurrence  of  alkali  spots  interrupts  the  continuity  of  fields 
and  orchards,  of  which  they  form  only  a  small  part,  but  enough 
to  mar  their  aspect  and  cultivation.  Their  increase  and  ex- 
pansion under  irrigation  frequently  renders  their  reclamation 
the  only  alternative  of  absolute  abandonment  of  the  invest- 
ments and  improvements  made,  and  from  that  point  of  view 
alone  it  is  of  no  slight  practical  importance.  Moreover,  the 
occurrence  of  vast  continuous  stretches  of  alkali  lands  within 
the  otherwise  most  eligibly  situated  valley  lands  of  the  irriga- 
tion region  forms  a  strong  incentive  towards  their  utilization. 


482 


SOILS. 


There  is,  however,  a  strong  intrinsic  reason  pointing  in  the 
same  direction,  namely,  the  almost  invariably  high  and  lasting 
productiveness  of  these  lands  when  once  rendered  available  to 
agriculture.  This  is  foreshadowed  by  the  usually  heavy  and 
luxuriant  growth  of  native  plants  around  the  margins  and  be- 
tween alkali  spots  (see  fig.  60)  ;  i.  e.,  wherever  the  amount 


ist  year,  zd  year,        3d  year,  Fourth  year — 42  bushels. 

-Fie.  75.— Wheat  grown  on  black  alkali  land  at  Tulare  Substation;  California,  showing  improve 
ment  in  successive  years  of  reclamation  treatment. 

of  injurious  salts  present  is  so  small  as  not  to  interfere  with 
the  utilization  of  the  abundant  store  of  plant-food  which,  under 
the  peculiar  conditions  of  soil-formation  in  arid  climates,  re- 
mains in  the  land  instead  of  being  washed  into  the  ocean. 
Extended  comparative  investigations  of  soil  composition,  as 
well  as  the  experience  of  thousands  of  years  in  the  oldest 
settled  countries  of  the  world,  demonstrate  this  fact  and  show 


UTILIZATION  AND  RECLAMATION  OF  ALKALI  LANDS.     483 

that  so  far  from  being  in  need  of  fertilization,  alkali  lands  usu- 
ally possess  extraordinary  productive  capacity  whenever  freed 
from  the  injurious  influence  of  the  excess  of  useless  salts  left 


in  the  soil  in  consequence  of  deficient  rainfall.     (See  analyses, 
chapter  22,  pp.  430,  437). 

Among  many  striking  examples  of  the  results  of  such  re- 
clamation, is  that  represented  in  the  annexed  figure   (75).  of 


484  SOILS. 

grain  grown  on  strong  alkali  land,  before  and  after  reclama- 
tion treatment.  On  the  original  land  even  "  alkali  weeds  " 
would  hardly  grow ;  while  afterward  a  wheat  crop  represent- 
ing forty-two  bushels  per  acre  was  grown.  Additional  illus- 
trations are  shown  in  the  second  figure  (76),  showing  crops  of 
wheat  and  barley  as  grown  on  partly  reclaimed  land  at  the 
Tulare  substation. 

While  it  is  certainly  true  that  when  rightly  treated,  alkali 
lands  can  be  rendered  profusely  and  lastingly  productive,  yet 
close  attention  and  constant  vigilance  are  needed  so  long  as  the 
salts  remain  in  the  soil;  and  no  one  not  determined  to  give 
such  land  such  full  attention,  should  undertake  to  cultivate  it. 


PART  FOURTH. 

SOILS  AND  NATIVE  VEGETATION. 


CHAPTER  XXIV.1 

THE  RECOGNITION  OF  CHARACTER  OF  SOILS  FROM  THEIR 
NATIVE  VEGETATION;  MISSISSIPPI. 

Climatic  and  Soil-Conditions. — Next  to  climatic  conditions, 
chief  among  which  are  temperature  and  moisture,  the  physical 
and  chemical  nature  of  the  soil  and  subsoil  is  the  most  potent 
factor  in  determining  the  natural  vegetation  of  any  region. 
The  limitations  we  observe  in  the  adaptation  of  cultivated  lands 
to  certain  crops,  even  with  artificial  help,  must  be  much  more 
strongly  pronounced  when  no  such  aid  is  given,  and  the  strug- 
gle for  the  survival  of  the  fittest  is  continued,  subject  only  to 
seasonal  variations,  for  thousands  of  years.  It  is  obvious  that 
within  the  limits  of  the  regional  flora,  the  natural  vegetation  of 
any  tract  represents  the  best  adaptation  of  plants  to  soils,  in 
the  results  of  long  periods  of  the  struggle  for  existence  be- 
tween competing  species;  the  survivors  being  those  best 
adapted  to  the  entire  environment. 

In  countries  uninhabited  by  man  the  chief  conditions  outside 
of  the  direct  influence  of  climate  and  soil  that  may  materially 
affect  the  results  of  the  competition  are  connected  with  the 
animal  creation;  and  within  the  latter,  insects  are  probably  the 
most  influential,  beneficially  in  the  part  they  play  in  the  fertil- 
ization of  flowers,  injuriously  in  their  role  as  parasites.  Since 
in  the  absence  of  man.  the  effects  of  fire  would  ordinarily  be 
conditioned  upon  the  occurrence  of  thunderstorms,  its  effects 
would  then  properly  come  under  the  head  of  climatic  influences. 
P>ut  while  these  and  some  other  disturbing  factors  must  not 
be  forgotten  in  considering  the  relations  of  soils  to  the 
natural  vegetation  borne  by  them,  the  common  consensus  of 
mankind  has  long  recognized  the  intimate  connection  existing 
between  the  two.  and  has  everywhere  made  it  the  basis  of  at 
least  a  general  estimate  of  the  agricultural  value  of  the  land 
concerned. 

1  The  special  object  of  this  chapter  as  a  whole  has  seemed  to  the  writer  to  re- 
quire a  repetition  of  much  that  is  already  said  in  the  preceding  chapters. 

4s; 


488  SOILS. 

NATURAL  VEGETATION   THE    BASIS   OF   AGRICULTURAL   LAND 
VALUES  IN  THE  UNITED  STATES.1 

In  countries  long  settled,  as  in  Europe,  where  the  nature  of 
the  original  forest  is  unknown  or  a  matter  of  tradition  only, 
the  adaptations  of  the  several  kinds  of  land  to  culture  plants 
and  forest  trees  has  been  gradually  ascertained  by  cultural  ex- 
perience, and  their  designations,  values  and  uses  determined 
accordingly.  In  the  United  States,  the  character  of  the  origi- 
nal forest  growth  is  mostly  in  evidence,  or  is  definitely  known 
by  tradition,  even  in  the  older  states.  West  of  the  Alleghenies, 
there  is  as  yet  little  difficulty  in  this  regard,  partly  because 
even  where  the  original  forest  growth  has  disappeared  its 
character  remains  on  record,  the  assessed  land  values  being 
very  commonly  based  upon  the  tree  growth  of  the  wild  land. 
In  the  Southern  States  especially,  the  classification  of  uplands 
into  "  pine  lands  "  and  "  oak  lands  "  is  universal,  and  is  associ- 
ated with  certain  limits  of  valuation,  both'  by  assessors  and 
purchasers.  Within  each  of  these  two  classes,  however,  there 
are  well-defined  gradations  of  cultural  value  according  to  the 
kind  (species)  e.  g.,  of  pine  or  oak  that  occupies  the  ground, 
either  alone,  or  in  intermixture  with  other  trees  whose  pres- 
ence or  absence  is  considered  significant.  In  the  case  of 
"  bottoms  "  or  alluvial  lands,  corresponding  distinctions  and 
classifications  obtain ;  we  hear  of  hickory,  beech,  gum,  and 
cherry  bottoms,  hackberry  hammocks,  etc.  each  name  being 
associated  with  certain  cultural  values  or  peculiarities  of  soil, 
well  understood  by  the  farming  population. 

INVESTIGATION    OF    CAUSES    GOVERNING   THE   DISTRIBUTION    OF 
NATIVE  VEGETATION. 

It  seems  singular  that  such  well  and  widely  understood 
designations  and  important  distinctions  should  not  long  ago 
have  been  made  the  subject  of  careful  investigation  and  pre- 
cise definition  by  agricultural  investigators.  For  apart  from 
their  practical  importance  as  guides  to  the  purchaser  of  land, 
or  settler,  this  correlation  of  land-values  and  natural  vegetation 
is  of  the  utmost  interest  in  offering  an  opportunity  for  re- 
searches on  the  factors  which  determine  the  choice  of  these 
several  trees  and  the  corresponding  shrubby  and  herbaceous 

1  See  above,  pp.  313  to  315,  chapter  18. 


RECOGNITION  OF  CHARACTER  OF  SOILS.  489 

growths.  Moreover,  the  cultural  results  and  adaptations 
corresponding  to  certain  natural  growths  being  known  from 
experience,  a  thorough  knowledge  of  the  soils  so  characterized 
should  enable  us  to  project  into  new  lands,  where  experience 
is  lacking,  the  benefits  of  experience  already  had ;  even  in  cases 
where,  from  some  cause,  the  natural  vegetation  is  different,  or 
absent.  Only  very  fragmentary  and  casual  observations  in 
this  line  are  on  record  thus  far,  almost  the  only  generally 
recognized  chemical  characterization  of  plant  habit  being  that 
of  calciphile  (lime-loving),  and  calcifuge  (lime-repelled)  ones, 
but  with  few  attempts  at  more  than  local  application.  Yet, 
to  ascertain  by  the  physical  and  chemical  examination  of  soils 
what  are  determining  factors  of  certain  natural  vegetative 
preferences,  which  are  invariably  followed  by  certain  agricul- 
tural results,  should  not  be  an  unsolvable  problem,  and  its 
practical  importance  should  justify  its  most  active  investiga- 
tion. 

Investigations  in  Mississippi. — In  his  explorations  connected 
with  the  Geological  and  Agricultural  Survey  of  the  State  of 
Mississippi,  as  well  as.  later  on,  in  similar  researches  carried 
on  in  other  states,  the  writer  was  forcibly  struck  with  the 
close  correspondence  of  the  limits  of  geological  formations 
with  those  of  vegetative  zones;  so  much  so  that  he  was  led  to 
rely  very  largely  on  the  latter  as  indicative  of  the  probable 
occurrence  of  outcrops  that  otherwise,  in  a  level  country,  would 
have  passed  unperceived. 

These  observations  upon  the  correlations  between  virgin 
soils  and  their  native  vegetation  having  originally  been  made 
by  the  writer,  in  great  detail,  in  the  state  of  Mississippi,  from 
1855  to  1872.  and  that  state  being  from  natural  causes  a  pecul- 
iarly cogent  illustration  of  such  correlation:  it  seems  advisable 
to  describe  first,  somewhat  in  detail,  the  facts  observed  there, 
and  subsequently  to  compare  them  with  what  has  been  observed 
elsewhere  by  him  or  others. 

No  claim  is  made  to  an  even  approximately  exhaustive  pres- 
entation of  the  whole  subject,  even  within  the  I'nited  States; 
nor  is  it  intended  to  give  complete  lists  of  vegetation.1  The 

1  Such  lists,  so  far  as  the  State  of  Mississippi  is  concerned,  may  be  found  in  the 
writer's  Report  on  the  Agriculture  and  (ieology  of  Mississippi,  1860.  See  also 
Plant  Life  of  Alabama,  by  Charles  Mohr. 


49° 


SOJLS. 


object  is  to  give  such  facts  as  have  been  fairly  well  established 
by  observation,  hoping  that  more  thorough  investigations  in 
the  same  line  will  thereby  be  stimulated. 

VEGETATIVE  BELTS  IN   NORTHERN   MISSISSIPPI. 

The  diagram  below  is  a  sketch-map  of  the  most  northern 
part  of  Mississippi,  showing  the  narrow  parallel  belts  of  suc- 
cessive geological  formations  or  terranes  running  north  and 
south,  wllich  bear  the  varying  zones  of  vegetation  character- 
istic of  each  one,  as  indicated  in  the  legend  beneath. 


FIG.  77. — Sketch  map  of  Soil  Belts  in  Northern  Mississippi,  east  and  west. 

SOIL  REGIONS  OF  NORTHERN  MISSISSIPPI,  SHOWING    CHANGES  FROM   EAST  TO 
WEST,   AND   LIME   PERCENTAGES  IN   SOILS. 


Lime,  p 

c. 

Soil  Character.                                                   Vegetation. 

I. 

.40— 

.60 

Clay  loams,  clay.                       Oaks,  sweet  gum,   tulip   tree,  walnut,   red  cedar, 

ash,  hickories. 

2. 

.05— 

.14 

Sandy  loams,  sands.                   Short-leaf  pine,  post,  scarlet  and  black-jack   oaks, 

black  gum,  chestnut. 

3- 

1.00  J 

.40 

"  White  lime  "  prairie  ;  clays  Red   cedar,   crab   apple,  Chickasaw   plum,   sturdy 

and  clay  loams.                           post  and  black-jack  oaks,  honey  locust. 

4- 

.30— 

•5° 

Mellow   red  loams  of  "  Pon-  Oaks,   hickories,   walnut,   tulip   tree,  ash,  cherry, 

totoc  ridge."                                umbrella  tree. 

5- 

.08— 

.18 

Heavy  gray  clay  soils,  some  Scrubby  post  and  black-jack  oak,   short-leaf   pine. 

gray   sands.      "  Flatwoods." 

6. 

•'5— 

.25  Sandy    ridges  and    uplands,  Post,  black-jack,   scarlet  and   upland  willow  oaks, 

broken.                                         small;  some  chestnut. 

7- 

.25— 

.35  Mellow  clay  loams  of  "Table  Fine  black,  red,  post,  Spanish  and  black-jack  oaks, 

I  lands."                                          hickories,  sweet  gum. 

8. 

2.00  —   5 

.00  Calcareous  sandy  silt,  "Bluff  Oaks  as  above,  tulip  tree,  ash,  honey  locust,  lin- 

9- 

96. 


.40— 

1.12  — 


.40 
.26— 


.40 


clay.  ;hackberry,  cane. 

Sandy  alluvium,  "  Frontland.  Sweet  gum,  maple,  willow  oak,  elm,  hackberry. 
Light  sandy   ioam   of  "  Dog-  Dogwood,  sweet  gum,  holly,  ash,  sassafras,  prickly 
wood  ridge."  near. 


Limestone  Belt, — Beginning  on  the  east  we  have,  first,  a  narrow  belt 
of  limestones  of  the  carboniferous  formation,  on  which  there  is  a  fine 


RECOGNITION  OF  CHARACTER   OF  SOILS. 


491 


growth  of  various  oaks,  with  walnut,  hickory,  sweet  gum,  tulip  tree  and 
red  cedar,  and  a  very  productive  soil. 

"  Pine  Hills." — Next  adjoining  on  the  west  comes  a  belt  of  sandy, 
non-calcareous  beds  of  the  lower  Cretaceous  formation,  about  18  miles 
wide.  It  has  a  hilly  surface,  and  outside  of  the  narrow  valleys,  the 
prevalent  timber  is  short-leaved  pine  and  scrubby  black-jack  oak,  with 
some  post  oak  and  small  black  gum,  and  a  few  large  chestnut  trees. 

"Prairie"  Belt. — Westward  of  this  belt  we  descend  into  a  level 
"prairie"  region,  six  to  twelve  miles  wide;  the  "white  lime  country," 
having  heavy  black  clay  soils,  underlaid  by  the  cretaceous  "  rotten  lime- 
stones ;"  which  are  profusely  productive.  The  sparse  tree  growth  con- 
sists of  stout,  vigorous  and  dense-topped  post  and  black-jack  oaks,  with 
clumps  of  crab  apple,  Chickasaw  plum  thickets,  and  an  occasional  red 
cedar. 

Pontotoc  Ridge. — West  of  the  prairie  belt  we  ascend  into  a  ridgy  hill 
country,  twelve  to  fourteen  miles  wide;  the  "  Pontotoc  ridge,"  formed 
of  the  soft  limestones  and  marls  of  the  upper  cretaceous  formation,  and 
covered  with  a  deep  red  soil,  which  bears  a  rich  growth  of  oaks,  with 
hickory  interspersed,  and  black  walnut,  umbrella  and  tulip  tree  even  on 
the  ridges.  This  is  one  of  the  finest  agricultural  regions  of  the  State. 

Flatwoods. — From  the  Pontotoc  ridge  and  its  fine  lands  and  timber 
we  descend  to  westward  into  the  "  Flatwoods "  belt,  three  to  eight 
miles  wide ;  a  level  country  underlaid  by  heavy  gray  non-calcareous 
clays  of  the  tertiary  formation,  from  which  most  of  its  soil  is  directly 
formed.  It  bears  a  pretty  dense  growth  of  the  same  species  of  oaks 
that  characterize  the  prairies  farther  east,  but  the  form,  habit  and  size 
of  the  trees  is  so  different  that  many  of  the  inhabitants  believe  them  to 
be  different  species.  The  black-jack  oak  looks  like  small,  dense-topped 
apple  trees ;  the  post  oak,  on  the  contrary,  has  an  open  top  of  the  form 
of  a  short-handled,  spreading  broom.  The  soil  is  poor  and  unthrifty, 
as  are  the  few  disappointed  settlers,  who  bought  the  land  on  the  strength 
of  its  oak-tree  gro\vth.  (See  p  ige  500). 

Brown  Loam  Region.  Table  Lands. — Adjoining  the  Flatwoods  on  the 
west  is  a  broad  upland  region,  with  a  brownish-yellow  soil  and  subsoil, 
extending  nearly  to  the  edge  of  the  Mississippi  bottom.  In  its  eastern 
portion  it  is  rather  broken  and  hilly,  with  sandy  ridge  soils,  a  mixed 
growth  of  oaks  and  short-leaved  pine,  and  occasional  chestnuts  ;  a  fair 
farming  country  only.  To  westward  the  ridges  become  lower  and 
broader,  assuming  a  plateau  character.  The  pine  disappears,  and  black, 
Spanish,  red  and  white  oak,  with  much  hickory,  largely  replaces  the 
black  jack  and  post  oak ;  thus  characterizing  the  fertile  brown-loam 


492 


SOILS. 


"  table-lands  "  that  extend  through  western  Tennessee  and  Mississippi 
into  Louisiana,  and  have  long  been  noted  for  their  high  production  oi 
fine  upland  cotton. 

Cane  Hills. — On  the  western  border  of  the  table-land  region,  and 
here  forming  a  strip  only  a  few  miles  wide  along  the  edge  of  the  Mis- 
sissippi bottom,  but  from  70  to  450  feet  above  it,  lies  the  remnant  of 
what  farther  south  constitutes  a  wide  and  important  agricultural  belt ; 
the  Bluff  or  Loess  formation,  locally  known  as  "  the  Cane  Hills."  The 
soil  is  largely  composed  of  grains  of  sand  and  silt  cemented  by  lime 
carbonate ;  it  is  therefore  calcareous,  and  as  on  the  Pontotoc  ridge, 
described  above,  we  find  here  the  black  walnut,  the  tulip  tree,  ash  and 
others,  elsewhere  restricted  to  the  alluvial  "  bottoms,"  on  the  ridges 
themselves,  from  sixty  to  a  hundred  feet  above  the  stream  beds. 

Mississippi  Bottom. — At  the  western  foot  of  this  bluff  there  lies  the 
great  Mississippi  Bottom,  with  its  rich  soils  and  varied  forest  growth. 
This  also,  however,  subdivides  into  at  least  three  distinct  soil  and  vege- 
tative zones,  viz.,  the  sandy  "  Frontlands,"  which  lie  on  the  immediate 
banks  of  the  great  river  and  its  main  branches,  and  the  heavy  clayey 
"  Back-land  "  areas,  whose  soils  are  partly  the  product  of  modern 
swamp  deposits  from  backwaters,  partly  result  from  the  disintegration 
of  strongly  calcareous  clays  constituting  the  lower  part  of  the  Bluff  or 
Loess  formation.  A  third  natural  subdivision  is  the  "  Dogwood  ridge," 
a  narrow  belt  of  slightly  elevated  land,  mostly  above  ordinary  overflows, 
which  extends  diagonally  from  the  Mississippi  river  to  the  Yazoo  bottom, 
and  seems  to  be  the  continuation  of  "  Crowleys  ridge  "  in  Arkansas. 
Each  of  these  soil  belts  has  its  own  characteristic  forest  growth,  as  in- 
dicated in  the  table  below  the  map. 

We  have  here  along  an  east-and-west  line  of  about  200 
miles,  eleven  markedly  distinct  zones  of  vegetation,  readily 
recognized  as  such  by  every  farmer,  and  each  underlaid  by  a 
distinct  geological  terrane.  It  does  seem  as  though  a  close 
study  of  these  and  of  the  soils  overlying  them  should  lead  to 
some  definite  results  showing  the  physico-chemical  causes  of 
these  differences. 

Lime  apparently  a  governing  Factor. — The  connection  of 
some  of  these  changes  in  vegetation  with  the  calcareous  nature 
of  the  corresponding  formation  has  already  been  referred  to. 
As  regards  four  of  the  eleven  divisions,  this  is  obvious  even  to 
the  casual  observer,  and  is  well  known  to  the  population,  who 


RECOGNITION  OF  CHARACTER  OF  SOILS. 


493 


speak  of  the  "  lime  country  "  or  belts  being,  as  a  matter  of 
common  knowledge,  the  best  land;  in  full  accord  with  what,  in 
Kentucky  and  elsewhere,  has  passed  into  a  popular  maxim.1 

Taking  as  a  guide  the  trees  and  plants  which  characterize 
the  obviously  calcareous  lands,  our  next  step  should  be  to 
verify,  if  possible,  the  fact  that  wherever  these  occur  naturally, 
lime  is  abundant  in  the  soil  in  comparison  with  those  lands  in 
which  such  vegetation  does  not  occur  naturally,  or  perhaps 
even  fails  to  flourish  when  planted  without  special  fertilization. 
This  the  writer  has  sought  to  do,  first  in  connection  with  the 
survey  work  of  the  state  of  Mississippi,  and  subsequently  in 
the  wider  field  that  has  since  come  under  his  observation. 

SOIL  BELTS  IX  SOUTHERN   MISSISSIPPI. 

In  Mississippi,  the  general  conclusions  derived  from  the  ob- 
servations made  on  the  northern  cross  section,  are  corroborated 
many  times  over  in  other  portions  of  the  state.  Aside  from  the 
cretaceous  prairie  region,  there  runs  across  the  middle  of  the 
state  a  belt  of  varying  width,  of  calcareous  tertiary  beds,  which 
also  give  rise  to  more  or  less  extensive  tracts  of  "  black 
prairie"  lands,  interspersed  with  non-calcareous,  mostly  sandy 
ridges,  the  lower  slopes  of  which,  influenced  by  the  calcareous 
beds,  bear  an  oak  and  hickory  growth,  while  the  higher  por- 
tions have  only  pine,  and  usually  remain  uncultivated.  South- 
ward of  this  "  central  prairie  "  belt  lies  the  long-leaf-pine 
forest  area  of  the  state,  underlaid  throughout  by  sandy,  non- 
cnlcareous  formations,  with  poor  sandy  soils,  save  here  and 
there  in  patches,  which  can  be  at  once  recognized  by  the  re- 
placement of  the  long-leaved  pine  by  a  vigorous  oak  growth; 
as  is  also  the  case  where  the  pine  area  abuts  against  the  calcare- 
ous "Cane  Hills"  on  the  west.  The  bottom  soils  of  this 
region  are  largely  "  sour."  and  bear  the  gallbcrry  ( I'riiios 
glabcr],  bay  galls  ( f'crsca  Carolina),  ti-ti  (Clifttviia  inouo- 
/>//V//(/),  candleberry  (Myricu  ccrifcra),  various  whortle- 
berries, the  pitcher  plants  (Sarraccnia) ,  yellow  star  grass 
(Alctris),  sundews,  Xyris,  Eriocaulon,  and  other  plants  of 
similar  habits. 

1  "  A  lime  country  is  a.  rich  country." 


494 


SOILS. 


Vegetative  and  Soil  Features  of  the  Mississippi  Coast  Belt. 
— South  of  the  long-leaf  pine  area  lie  the  coast  flats,  with  sour 
sandy  soils  underlaid  by  stiff  clays.  On  these  "  pine  mead- 
ows "  of  the  Mississippi  coast  occur  some  of  the  most  striking 
cases  of  modifications  of  vegetation  due  to  physical  and  chem- 
ical causes. 

As  is  well  known,  the  long-leaved  pine  habitually  belongs  to 
the  dry  sandy  uplands  of  the  Gulf  States;  the  deciduous  cy- 
press, on  the  other  hand,  is  most  characteristic  of  the  swamps, 
where  its  roots  are  permanently  submerged  in  water.  But  on 
the  pine  meadows  of  the  Mississippi  coast  we  see  these  two 
incongruous  trees  growing  side  by  side,  though  sadly  wrorsted 
by  their  mutual  concessions ;  their  heights  usually  ranging  from 
12  to  15,  rarely  as  much  as  18  feet.1  Yet  both  preserve  their 
characteristic  forms,  the  cypress  being  an  exact  miniature  re- 
production of  the  usual  level-topped  swamp  form,  except  as  to 
the  "  knee  "  feature;  while  the  pine  differs  only  in  stature  from 
its  giant  brethren  of  the  pine  hills,  from  which  it  can  be  traced 
down  through  all  grades  of  transition.  The  soil  on  which  this 
growth  occurs  is  a  sour,  sandy  one,  one  and  a  half  to  three  feet 
in  depth,  underlaid  by  a  solid,  impervious  gray  clay,  above 
which  is  usually  found  several  inches  of  coffee-colored  bottom 
water,  which  drains  slowly  into  the  sluggish  water-courses, 
themselves  carrying  brownish,  sour,  but  very  clear  waters. 
Analysis  shows  the  soil  to  be  sour  and  extremely  poor,  especi- 
ally in  its  lime  and  phosphates  (see  chapter  19,  p.  352)  ;  its 

1  R.  M.  Harper,  who  has  graphically  described  the  vegetative  features  of  the 
coastal  plain  of  Georgia  (Contr.  from  the  Dep.  of  Bot.  Colum.  Univ.  Nos.  192, 
215,  216,  1902-05;  also  Bull.  Torr.  Bot.  Club  29-32),  claims  the  deciduous  cypress 
of  the  wet  pine-barrens  and  ponds  therein,  the  vegetation  of  which  greatly  re- 
sembles that  of  the  pine  meadows  of  the  Mississippi  seacoast,  to  be  a  distinct 
species,  Taxodium  imbricarium,  the  leaves  of  which  are  imbricated,  instead  of 
two-ranked  and  with  spreading  leaflets.  He  supports  this  distinction  mainly  by 
the  differences  in  habit  from  the  Louisiana  swamp  cypress,  and  the  fact  that  the 
imbricated  form  occurs  wholly  on  non-calcareous  land,  while  the  other  is  at  home 
in  the  calcareous  alluvial  areas.  The  imbricated  form  has  been  observed  and 
commented  on  before,  as  a  mere  ecological  variation,  and  in  the  writer's  opinion 
this  is  ail  that  can  be  claimed,  in  view  of  the  much  greater  differences  in  the  form 
of  other  trees,  notably  oaks,  illustrated  below,  caused  also  by  lime.  There  would. 
h  fortiori^  be  reason  for  claiming  at  least  three  different  species  of  post  oak  and 
black-jack  (and  two  of  willow  oak),  which  differ  not  only  in  tree  form  but  also  in 
the  form  and  number  of  leaf  lobes,  and  yet  can  be  traced  into  one  another  by 
innumerable  transition  forms.  If  new  species  are  to  be  established  on  such  grounds, 
it  is  hard  to  see  where  the  variations  manifestly  due  to  environment  are  to  come  in. 


RECOGNITION  OF  CHARACTER  OF  SOILS.  495 

herbaceous  vegetation  consists  exclusively  of  very  small-seeded, 
"  calcifuge  "  plants  (sedges,  orchids,  Juncus,  Haemodoraceas, 
Xyris,  Polygala,  etc.).  This  land  is  wholly  unproductive  and 
affords  but  indifferent  pasturage,  except  the  first  season  after 
burning-over ;  probably  because  of  the  effect  of  the  minute 
amount  of  ashes  so  added.  As  the  coast  is  approached,  the 
clay  subsoil  has  an  increasing  depth  of  sandy  soil-mass  above 
it,  and  on  these  "  sand  hammocks  ''  the  long-leaved  pine  grad- 
ually assumes  more  and  more  of  its  usual  stature ;  the  cypress 
disappears,  and  the  Cuban  pine  (here  called  pitch  pine)  grad- 
ually comes  in ;  while  the  sedgy  vegetation  diminishes  and 
finally  disappears.  On  this  land  crops  may  be  grown  as  in  the 
long-leaf-pine  uplands. 

But  on  the  immediate  coast,  evidently  under  the  influence  of 
the  aboriginal  "  shell  mounds,"  the  yellow  sandy  soil  becomes 
blackish  from  the  (humus- forming)  effect  of  the  lime  thus 
supplied  ;  and  concurrently  the  coast  liveoak  (  Q.  t'ircns) ,  grape 
vines,  the  Hercules  club  (Aralla  spiuosa).  '*  1'herbe  a  tmis 
quarts"  (I'crbesina  sp. ),  and  numerous  leguminous  plants 
(which  are  wholly  absent  from  the  pine  meadows)  take  pos- 
session of  the  land,  which  is  very  productive  and  has  been 
specially  utilized  in  the  growing  of  Sea  Island  cotton.  Here 
the  clay  stratum  is  15  to  20  feet  below  the  surface,  and  roots 
penetrate  to  great  depths  in  the  pervious  soil,  whose  great 
thickness  makes  up  for  its  low  percentage  of  plant-food  (see 
table  below).  This  land  is  distinctly  limited  by  the  extent  of 
the  shell  heaps,  past  or  present,  and  shows  a  respectable  per- 
centage of  lime. 

PINE  MCADOWS  SANO  HAMMOCKS  SfAlSLANO 

COTTON  50IL 


—  — ~  Black-  Cloy -with-  OyJlers-and-Cypress^Snjmp^  ^-^ 

FK;.  78.— Schematic  profile  of  tlic  Mississippi  Coast  Belt,  through  Jackson  County. 

The  annexed   schematic   profile    (fig.    78)    illustrates   these 
changes  of  soil  and  vegetation,  which  furnish  a  striking  ex- 


496  SOILS. 

ample  of  the  effective  modification  of  vegetative  features  by 
physical  and  chemical  soil-conditions. 

It  would  be  difficult  to  find  a  more  striking  exemplification 
of  the  effect  of  lime  carbonate,  not  only  upon  the  vegetation 
but  also  upon  the  physical  and  chemical  characters  of  the  hope- 
lessly unproductive  soil  of  the  sand  hammocks  and  pine  mead- 
ows; no  longer  brown  and  sour,  but  jet  black  and  neutral, 
modifying  favorably  every  physical  quality.  Humus  likewise 
nowhere  shows  its  benefits  more  strikingly. 

Table  of  Lime-Percentages. — The  table  below  shows  the 
average  lime  percentages  observed  in  most  of  the  several  vege- 
tative areas  mentioned  above.  To  meet  the  objection  some- 
times made  that  the  vegetative  changes  noted  may  be  due  to 
the  larger  amounts  of  phosphoric  acid  and  potash  frequently 
found  in  calcareous  lands,  the  percentages  of  the  latter  are  also 
given.  Considering  the  origin  of  limestones,  such  a  connec- 
tion is  not  unexpected,  but  it  is  far  from  constant.  On  the 
contrary,  the  frequent  co-occurrence  of  much  lime  and  high 
production  with  small  percentages  of  phosphoric  acid  and 
potash  leads  to  the  conclusion,  already  discussed  ( see  chapter 
19,  p.  365),  that  in  presence  of  abundance  of  calcic  carbonate, 
smaller  percentages  of  phosphoric  acid  may  be  considered  ade- 
quate than  when  lime  is  deficient,  on  account  of  greater  avail- 
ability. Almost  the  same  may  be  said  of  potash ;  and  it  is 
quite  possible  that  the  presence  of  large  amounts  of  lime  tends 
to  prevent  the  leaching-out  of  this  base,  in  consequence  of 
greater  facility  for  the  formation  of  zeolites.  Illustrations  of 
this  kind  have  already  been  given  (chapters  3,  22). 

Definition  of  "  Calcareous  Soils." — It  will  be  noted  that  the 
very  obvious  and  important  changes  of  vegetation  are  brought 
about  by  comparatively  slight  differences  in  lime-content.  In 
fact,  only  two  of  the  soils  enumerated  above  would,  according 
to  the  estimates  usually  given  in  books  on  soil  composition,  be 
considered  as  properly  calcareous.  But  the  decisive  feature 
in  this  matter  must  evidently  be  the  native  vegetation,  which 
expresses  the  nature  of  the  land  much  more  clearly  and  author- 
itatively than  any  arbitrary  definition  or  nomenclature  can 
possibly  claim  to  do.  A  soil  must  be  considered  as  being  cal- 
careous whenez'cr  it  naturally  supports  the  vegetation  char- 
acteristic of  calcareous  soils. 


RECOGNITION    OF  CHARACTER  OF  SOILS. 


497 


u  u     -c~ 


-  p 


•7    .  4i 


C  -C    r~ 


3-' 


_:     | 


498  SOILS. 

DIFFERENCES  IN  THE  FORM   AND  DEVELOPMENT   OF  TREES.1 

It  will  be  noted  that  in  the  above  table,  as  well  as  in  the  dis- 
cussion preceding  it,  identical  species  of  trees  are  ascribed  to 
vegetative  areas  of  widely  different  productive  capacity.  Per- 
haps the  most  striking  example  is  that  the  cretaceous  prairies 
and  the  adjoining  flatwoods  belt,  standing  respectively  highest 
and  lowest  in  the  scale  of  productiveness,  are  yet  bearing 
specifically  identical  tree-growth,  to-wit,  the  post  oak  (Quercus 
minor)  and  the  black-jack  oak  (Q.  marylandica) .  While  to 
the  field  botanist  2  there  can  be  no  question  as  to  the  absolute 
specific  identity  of  the  two  trees  as  growing  on  the  respective 
areas,  yet  the  mode  of  development  of  both  is  so  different  in 
the  two  cases,  that,  as  before  remarked  they  are  popularly  sup- 
posed to  be  different  "  kinds." 

Forms  of  the  Post  Oak. — The  post  oak  of  the  prairie  lands  is 
a  tree  50  to  70  feet  high,  with  a  stout,  excurrent,  rather  conical 
trunk,  often  somewhat  curved  to  one  side  above,  and  densely 
clothed  from  within  12  or  15  feet  of  the  ground  with  com- 
paratively short,  sturdy  branches  set  squarely  to  the  trunk, 
much  crooked  (geniculate),  often  reflexed  downward;  alto- 
gether forming  a  dense  head,  beneath  whose  thick  foliage,  a 
bird  or  squirrel  is  quite  secure  from  the  hunter's  aim. — In  the 
flatwoods,  on  the  contrary,  the  post  oak  has  a  thin,  rather  short 
trunk,  divided  up  at  15  or  20  feet  height  into  long,  rod-like 
branches,  spreading  broom-fashion,  and  scantily  clothed  with 

1  It  is  a  matter  of  regret  to  the  writer  that  owing  to  the  long  distance  intervening 
and  the  difficulty  of  securing  competent  and  sympathetic  observers  for  such  work, 
it  has  not  been  possible  for  him  to  secure  photographs  of  the  tree-forms  here  dis- 
cussed.    At  the  time    his  own  observations  were  made,  photography  was  prac- 
tically unavailable  as  yet,  and  the  figures  given  are  therefore  based  upon  sketches 
made  at  the  time,  and  partly  upon  recollection.     They  represent  types  rather  than 
definite  individuals,  which  were   however  described  when  fresh  in  mind,  in  the 
Report  on  the  Agriculture  and  Geology  of  Mississippi,  1860,  pages  254  et  seq. 

2  It  has  been  already,  and  doubtless  will  be  again  and  increasingly,  attempted  to 
make   distinct  "  species  "  of  these   widely  different   forms  of  trees.     But   this  is 
simply  begging  the  question.     Mere  external  diagnostic  marks  will  not  avail  here ; 
it  would  have  to  be  shown  that  the  seed  of  these  different  forms  do  not  produce 
the  other  forms  under  changed  conditions.     Until  this  has  been  done,  the  number- 
less  transition  forms  which  he  that  runs  may  observe  in  the  field,  throw  upon  the 
species-makers  the  onus  of  proof  of  differences  of  specific  value — if  it  be  possible 
to  define  such  value. 


RECOGiNITION  OF  CHARACTER  OF  SOILS.  499 

short  twigs  bearing  tufts  of  leaves ;  thus  forming  an  open  head, 
in  which  no  creature  can  hide  effectually.  On  the  brown-loam 
table-lands,  again,  the  post  oak  has  a  straight,  rather  slender, 
excurrent  trunk  with  long  and  more  or  less  crooked  limbs  pro- 
jecting at  a  large  angle,  sometimes  even  drooping,  and  freely 
divided  up  into  lateral,  leafy  branches;  the  trees  attain  from 
40  to  55  feet  in  height.  Again,  on  the  high  sandy  ridges 
which  are  interspersed  in  the  eastern  portion  of  the  brown  loam 
area,  we  find,  generally  associated  with  a  similarly  depauper- 
ated form  of  the  black-jack  oak,  and  with  the  Upland  Wil- 
low oak  ( O.  ciiierca),  a  form  of  the  post  oak  intermediate  be- 
tween that  of  the  Flatwoods  and  the  Table  lands ;  twelve  to 
fifteen  feet  high,  with  thin  trunk,  "  sprangling  "  long,  crooked 
branches,  clothed  with  sparse  tufts  of  leaves.  These  four 
strikingly  distinct  types  are  shown  schematically,  in  their  ex- 
treme development,  in  the  subjoined  figures. 

It  is  hardly  necessary  to  say  that  between  these  extreme 
forms  there  are  many  degrees  of  transition,  corresponding  to 
the  transitions  between  the  several  soil-classes  respectively  rep- 
resented by  them;  or  they  may  be  developed  into  depauperated 
types.  Thus,  for  example,  the  forms  of  the  post  and  black-jack 
oak  found  on  the  sandy  ridges  of  the  yellow  loam  region, 
hardly  need  experience  in  the  observer  to  interpret  them  as 
characterizing  a  wretchedly  poor  soil. 

Forms  of  the  Black-jack  Oak. — Xot  les-^  striking  are  the 
characteristics  of  the  forms  of  the  black-jack  oak  as  developed 
upon  these  several  kinds  of  land.  The  black-jack  of  the  prai- 
ries is  a  low  tree  with  a  dense  rounded  head,  often  somewhat 
flattened  above,  and  a  low,  thick-set  trunk  divided  up  into 
square-set  branches,  so  densely  clad  with  foliage  that  no  light 
penetrates  into  the  interior,  and  birds  can  safely  hide  and  nest 
within  it.  The  height  rarely  exceeds  35  feet,  the  head  being 
20  to  30  feet  across. 

The  Flatwoods  form,  on  the  contrary,  rarely  exceeds  i; 
feet  in  height,  with  a  very  rough  bark  and  a  small,  rather 
dense,  rounded  top.  giving  the  whole  the  appearance  of  a  small 
apple  tree.  Practically  the  same  form  is  seen  on  poor,  clay 
ridges  of  "  hogwallow  "  land. 

On  the  brown-loam  lands  the  black-jack,  like  the  p<>st  oak, 
has  a  rather  slender,  often  somewhat  crooked,  but  excurrent 


500 


SOILS. 


I 

ui  '5 
1  I 


"j*  •''Aipii.p?' 


>.  o 
"H  '*• 


-JLC 


RECOGNITION   OF  CHARACTER  OF  SOILS. 


501 


trunk  35  to  50  feet  high,  with  more  or  less  crooked  limbs  of 
moderate  length,  well  provided  with  leafy  branches,  but  form- 
ing altogether  a  rather  open  crown.  A  depauperated  form  of 


_..._ 


• 


.§> 


this  tyne  occurs  on  the  sandy  ridges  of  the  yellow-loam  region 
and  is  u  to  15  feet  high,  with  slender,  crooked  1  (ranches, 
clothed  with  scanty  foliage:  as  shown  in  Figure  Xo.  80.  along- 
side of  the  other  typical  forms 


502  SOILS. 

In  all  these  variations  of  the  tree  forms,  there  is  also  a  con- 
comitant variation  in  the  forms  and  other  characters  of  the 
leaves.  Thus  in  the  compact  forms  of  the  black-jack  oak,  the 
trilobate  leaf  is  almost  completely  obliterated,  the  leaf  being 
simply  rounded-cuneate,  somewhat  auriculate  at  base.  In  the 
sparse-branched  upland  forms  the  leaves  are  deeply  three- 
lobed,  and  the  ferruginous  tomentum  of  the  lower  surface  is 
much  less  pronounced.  The  lobation  of  the  post  oak  also 
varies  considerably  both  in  the  numbers  of  lobes  and  in  their 
obtuseness.  Similar  differences  prevail  in  the  case  of  the 
black  and  Spanish  oaks;  thus  in  the  latter,  the  long  terminal, 
falcate  lobe  is  always  most  pronounced  on  "  rich  "  soils,  while 
on  poor  ones  the  trilobate  leaf  predominates. 

Of  course  all  these  forms  may  be  found  bearing  acorns,  so 
that  they  undoubtedly  represent  adult  trees. 

Characteristic  Forms  of  other  Oaks. — Similar  general  fea- 
tures are  repeated  in  the  case  of  the  other  species  of  oaks,  and 
also  more  or  less  in  other  kinds  of  trees;  though  mostly  less 
pronouncedly  than  with  the  two  species  above  described. 
Among  the  more  striking  are  the  two  forms  of  the  willow  oak 
(Q.  phellos),  which  on  low,  undrained  ground  assumes  the 
low,  rounded,  "  apple-tree  "  form,  while  on  well-drained  up- 
lands of  good  fertility  it  is  a  beautiful,  slender  tree  producing 
almost  the  effect  of  the  acacia  type;  it  is  then  a  sign  of  first- 
class  land.  The  scarlet  oak  rather  reverses  these  stypes;  on 
good,  "  brown-loam  "  upland  it  is  of  rounded  form,  not  very 
tall,  with  sturdy,  rough-barked  trunk ;  while  on  poor  hillside 
lands  its  tall,  smooth,  white  trunk  stands  out  as  a  conspicuous 
admonition  to  the  landseeker  to  beware  of  a  poor  purchase. 
The  black  and  Spanish  oaks  also  indicate,  by  tall  thin  trunks, 
a  deterioration  of  the  land  as  compared  with  the  lower  and 
more  sturdy  growth  on  areas  relatively  richer  in  lime. 

Sturdy  Growth  on  Calcareous  Lands. — One  feature  invari- 
ably repeated,  not  only  in  Mississippi  but  throughout  the 
United  States,  is  that  /;/  man\  strongly  calcareous  soils  the 
growth  of  all  trees,  as  well  as  of  shrubs  and  of  many  herbace- 
ous plants,  is  of  a  more  sturdy  and  thick-set  habit  than  that 
of  the  same  species  grown  on  thin,  sandy,  or  generally  on  non- 
calcareous  land.  This  effect  is  quite  as  apparent  in  the  arid 


RECOGNITION  OF  CHARACTER  OF  SOILS.  503 

region  of  the  Pacific  Coast  as  in  the  Atlantic  States,  on  the 
prairies  of  the  Middle  West,  and  of  the  Gulf  Coast.  The  ex- 
perienced farmer  recognizes  this  habit  of  the  tree-growth  as  a 
sign  of  good  land,  and  the  reverse,  viz.,  trees  of  lank,  tall  and 
thin  growth,  as  evidence  to  the  contrary,  from  the  Atlantic  to 
the  Pacific. 

Cotton  Plant. — The  cotton  plant  affords  very  striking  evi- 
dences of  this  influence  of  lime.  On  the  bottom  lands  of  a 
creek  in  Rankin  county.  Mississippi,  the  writer  found  a 
"  patch  "  of  cotton  with  luxuriant  stalks  reaching  above  the 
head  of  a  man  on  horseback,  but  almost  devoid  of  "  squares  " 
or  blooms.  The  soil  was  very  dark  and  rich-looking,  but  was 
derived  from  a  non-calcareous  tertiary  terrane  surrounding  the 
heads  of  the  stream.  A  few  rods  below,  the  latter  crosses  the 
line  of  a  calcareous  terrane,  from  which  copious  marly  debris 
have  been  washed  down  on  the  bottom  soil.  Here  the  cotton 
was  just  half  as  high  as  above,  and  thickly  covered  with 
squares,  blooms,  and  bolls. 

Another  similar  example  was  noted  on  the  Chickasawhay 
river,  in  \\ayne  county.  Miss,  \\here  that  stream  flows 
through  the  non-calcareous,  lignitiferous  area  of  the  tertiary 
formation,  its  bottom  lands  bear  cotton  crops  of  medium  pro- 
ductiveness only,  the  stalks  being  of  the  usual  height  of  about 
three  feet,  and  only  fairly  boiled.  Hut  a  short  distance  below 
the  point  where  the  soft  marls  of  the  marine  tertiary  are  cut 
into  by  the  stream,  the  cotton  plants  on  the  bottom  lands  are 
from  1 8  to  jo  inches  high  only,  closely  branched,  and  literally 
thronged  with  cotton  bolls,  so  that  the  fields  appear  a  solid 
mass  of  white.  The  only  objection  urged  against  this  land  is 
that  to  pick  such  cotton  "breaks  the  backs"  of  the  pickers. 
The  tree  growth  of  the  bottom,  of  course  shows  a  correspond- 
ing change. 

Lime  Fai'ors  Fruiting. — In  connection  with  the  obvious 
changes  of  form  and  stature  caused  by  the  presence  of  an 
abundant  supply  of  lime  carbonate  in  soils,  there  is  another 
that  has  been  long  noted  in  cultivation,  but  is  no  less  striking 
in  the  native  vegetation.  The  abundant  fruiting  of  oaks  on 
such  lands  as  compared  with  the  same  species  on  non-cal- 
careous soils  is  a  matter  of  common  note  in  the  Mississippi 


504  SOILS. 

Valley  states ;  and  the  same  is  true  of  other  trees,  and  of  her- 
baceous plants  as  well.  The  fruit  on  the  lime  soils  is  often 
smaller,  unless  much  humus  is  present ;  but  the  statement  made 
in  Europe  that  cultivated  fruits,  and  especially  grapes,  are 
sweeter  on  calcareou=  lands,  is  abundantly  verified  in  the  native 
fruits  of  the  Mississippi  Valley  states  as  well ;  where  the  various 
wild  berries,  haws,  plums,  etc.,  are  well  known  to  the  younger 
part  of  the  population  to  be  much  sweeter  and  higher-flavored 
in  certain  (calcareous)  localities  than  in  others,  besides  being 
usually  more  abundant. 

This  is  entirely  in  accord  with  the  well-known  fact  that  the 
application  of  lime  checks  the  excessive  wood  and  leaf  growth 
resulting  from  excess  of  nitrogen  as  well  as  moisture ;  while  on 
the  other  hand,  the  injurious  effects  of  overdressing  with  lime 
or  marl  are  known  to  be  repressed  by  the  use  of  stable  manure, 
or  by  green-manuring.  The  repression  of  excessive  wood 
growth  by  lime  would  seem  to  offer  a  simple  explanation  of  the 
compact  habit  of  growth  on  calcareous  lands ;  and  the  extraor- 
dinary sweetness  of  fruits  grown  in  the  arid  region  as  com- 
pared with  the  same  in  the  humid,  is  fully  in  accord  with  the 
high  lime-content  of  the  arid  lands. 

Stunted  Groi^tJi. — In  practice  it  will  be  found  in  most  cases 
that  a  stunted  native  growth  is  clue  not  so  much  to  lack  of 
plant-food  in  the  soil,  as  to  unfavorable  physical  conditions. 
Among  these,  shalhrnnicss,  and  extreme  heaviness  of  the  soil 
are  the  most  common  causes.  The  "  scab  lands,"  underlaid  by 
impervious  rock  at  a  depth  too  slight  for  culture  plants,  as  in 
many  plateaus  of  the  Pacific  Northwest,  and  in  rocky  or  mount- 
ainous regions  generally,  are  cases  in  point.  Strata  of  imper- 
vious clay  often  produce  the  same  result ;  but  in  this  case, 
should  such  clay  be  intrinsically  capable  of  supporting  plant 
growth,  the  land  can  often  be  made  available  for  orchard  pur- 
poses by  blasting  with  dynamite  (see  chapter  10,  p.  181). 

The  post  oak  (  and  black-jack)  flats  of  the  Mississippi  Valley 
states  are  familiar  examples  of  land  whose  dwarfed  tree  growth 
causes  it  to  be  avoided  by  settlers ;  similarly,  a  dwarfed  growth 
of  red  elm  (Ulinus  nibra],  hack-berry  and  ash  indicates  in  the 
flood  plain  of  the  Red  river  of  Louisiana  a  heavy  "  waxy  "  red 
clay,  or  "  gumbo  "  land,  scarcely  available  for  agricultural  pur- 


RECOGNITION  OF    CHARACTER  OF  SOILS. 


505 


poses.1  The  gray  or  white  "  crayfishy  "  bottom  and  bench 
lands  of  the  Southwestern  States,  so  poor  in  lime,  phosphates 
and  humus  as  to  be  worthless  under  existing  conditions,  are 
characterized  by  an  easily  recognized  scrubby  growth  of  Water 
and  Willow  Oaks  (0.  nigra,  or  aquatica,  and  phellos),  with 
low,  rounded  tops;  while  the  same  trees,  when  well  developed, 
indicate  highly  productive  lands. 

Physical  vs.  Chemical  Causes  of  Vegetative  Features. — The 
extent  to  which  the  modifications  of  form  alluded  to  above  are 
referable  to  chemical  and  physical  causes  respectively,  can  be 
approached  by  the  discussion  of  the  presence  or  absence  of  cer- 
tain trees  from  soils  of  extreme  physical  character,  but  other- 
wise normally  constituted.  As  has  been  shown  above,  the 
black-jack  and  post  oaks  belong,  as  species,  equally  to  the 
heaviest  and  lightest  soils  within  the  state  of  Mississippi ;  to 
the  black  and  yellow  "  prairie  "  soils,  as  well  as  to  the  sandy 
ridges  of  the  yellow-loam  region  :  showing  for  these  two  species 
as  such,  an  independence  of  physical  conditions  and  an  ex- 
traordinary adaptability,  found  in  few  other  trees.  They  are 
frequently  found  either  alone  or  associated  with  only  a  few 
other  species  of  local  adaptation,  such  as,  in  the  prairie  lands, 
the  crab-apple,  wild  plum,  and  the  juniper  or  red  cedar.  On 
the  soils  of  intermediate  or  loam  character,  on  the  contrary, 
they  are  always  associated  with  other  oaks  as  well  as  with 
hickory,  and  in  that  association  attain  what  may  be  considered 
their  normal  type  or  form. 

From  the  fact  that  the  dense,  rounded  top  is  formed  by  the 
black-jack  oak  both  on  the  rich  prairie  lands  and  on  the  poor 
soils  of  the  Flat  woods,  it  would  seem  that  that  form  is  the  out- 
come of  a  physical  cause.  viz.  the  extreme  "  heavy-clay  "  char- 
acter of  both  kinds  of  land:  and  we  may  note  that  exactly  the 
the  reverse  effect  is  observed  in  the  form  growing  on  the  poor 
sandy  ridges,  as  sho\vn  in  tig's  ~()  and  8:>.  Yet  it  will  also  be 
noted  that  in  the  case  of  the  post  oak,  the  poor,  heavy-clay 
soil  of  the  Flatuoods  produces  an  open,  broom-shaped  top 
while  the  form  assumed  on  the  sandy  ridges  is  substantially  the 
same  for  both  species.  Care  must  therefore  be  exercised  in 
drawing  general  conclusions  as  to  the  effects  produced  by 
either  physical  or  chemical  causes.  <//<>//('.  upon  tree  forms. 
1  Rep.  of  Cieologieal  Reconnoissance  of  Louisiana  ;  New  <  Mle.ins,  1873,  p.  27. 


506  SOILS. 

Lowland  Tree  Growth. — The  variations  occurring  in  the  val- 
leys or  alluvial  bottoms  are  less  obvious  to  superficial  observa- 
tion, yet  equally  important  and  cogent  to  the  close  observer. 
In  the  properly  alluvial  lands,  one  dominant  condition,  that  of 
adequate  moisture  supply,  is  almost  always  fulfilled,  irrespec- 
tive of  soil  quality.  In  addition  to  this,  as  stated  in  chapter 
2  (see  page  24),  practically  all  the  alluvial  lands  of  the 
humid  region  may  be  considered  as  being  of  a  more  or  less  cal- 
careous character,  as  compared  with  the  adjacent  uplands. 
These  two  important  conditions  dominate  in  a  great  measure 
the  minor  ones  of  variation  in  soil-texture.  Yet  where,  as 
is  largely  the  case  in  the  southern  part  of  the  State  of  Missis- 
sippi, the  amount  of  calcic  carbonate  is  insufficient  to  overcome 
the  sourness  of  the  soil,  the  vegetative  contrasts  become  ex- 
tremely striking  and  characteristic,  as  explained  above. 

Contrast  Between  "  First  "  and  "  Second  "  Bottoms. — A 
very  striking  phase  of  transition  between  the  alluvial  bottoms 
and  the  uplands  proper  in  the  Cotton  States  are  the  second  bot- 
toms or  hammocks  of  the  streams,  whose  soil  and  tree-growth 
in  most  cases  differ  markedly  from  those  of  the  first  bottom ; 
and  these  being  usually  closely  adjacent,  often  afford  a  very 
striking  contrast  to  the  latter.  From  some  antecedent  geologi- 
cal cause  not  fully  understood,  these  hammocks,  usually  ele- 
vated from  4  to  10  feet  above  the  present  flood  plain,  have 
almost  throughout  soils  of  a  fine  sandy,  pulverulent  or  silty 
nature,  frequently  in  strong  contrast  to  heavy  clay  soils  in  the 
first  bottom. 

They  seem,  moreover,  to  have  been  at  some  time  subject  to 
prolonged  maceration  under  water,  resulting  in  the  reduction 
of  the  ferric  oxid,  and  its  accumulation  in  the  lower  portion 
of  the  deposit  in  the  form  of  bog-ore  spots  or  "  black  gravel." 
Since  such  a  process  always  results  in  the  abstraction  of  phos- 
phoric acid  from  the  general  mass  of  the  soil,  to  be  accumulated 
in  the  bog  ore  in  an  inert  condition,1  these  hammock  soils, 
usually  whitish  or  gray  in  color,  are  almost  throughout  poor 
in  phosphates  as  well  as  in  lime;  the  latter  having  been  defini- 
tively leached  out.  The  resulting  vegetation,  as  may  be 
imagined,  is  widely  different  from  that  of  the  bottom  proper, 

1  See  Chapter  2,  p.  24. 


RECOGNITION  OF    CHARACTER  OF  SOILS. 


507 


as  well  as,  frequently,  from  that  of  the  adjacent  uplands;  and 
though  level  and  fair  to  see,  these  hammocks  are  usually  un- 
thrifty and  last  but  a  short  time  under  exhaustive  cultivation. 
Accordingly,  their  forest  growth  is  prevalently  that  of  the 
poorer  class  of  uplands,  viz.,  small-sized  post  and  black-jack 
oaks,  and  in  the  low  ground  depauperated  water  oak,  or  less 
commonly  willow  oak,  of  the  low,  stunted  type  indicative  of  a 
a  soil  of  inferior  productiveness.  The  luxuriant  growth  of  the 
present  alluvial  bottom  is  often  seen  within  a  few  feet  of  the 
unthrifty  vegetation  of  these  hammocks.  It  is  usually  only  in 
the  limestone  regions,  and  in  the  lower  course  of  the  larger 
streams,  that  the  hammocks  or  second  bottoms  are  found  to  be 
of  good  fertility. 

The  Tree  Growth  of  the  First  Bottoms.  The  Cypress.— 
Among  the  trees  occupying  the  low  ground  of  the  first  bottom 
in  the  southern  Mississippi  states,  the  deciduous  cypress  (  Tax- 
odium  distichmn)  deserves  special  mention  as  an  example  of 
extreme  variation  in  form.  In  sloughs  and  swampy  tracts,  as 
is  well  known,  the  cypress  grows  with  roots  submerged 
throughout  the  season,  excepting  only  the  excrescences  known 
as  "  knees,"  which  project  above  the  water,  probably  perform- 
ing some  function  in  connection  with  the  aeration  of  the  root, 
which  is  essential  to  the  root  functions  in  all  plants.  The 
trunk  rising  from  the  water  is  supported  by  numerous  pro- 
jecting buttresses  for  from  8  to  15  feet  above  the  water:  higher 
up  it  becomes  cylindrical  for  a  height  of  from  40  to  70  feet, 
then  divides  up  into  a  few  widely  spreading,  thick,  almost 
conical  branches,  whose  twigs  and  foliage  form  an  almost  level 
surface  to  the  head.  This  level-topped  forest  growth  char- 
acterizes at  once  the  submerged  areas  of  the  river  and  coast 
swamps. 

But  the  cypress  is  by  no  means  confined  to  the  swamps  and 
sloughs;  it  is  also  found  occupying  the  better  class  of  hammock 
lands,  u  or  i^  feet  above  water  level.  In  this  case,  however, 
the  tree  assumes  a  shape  and  growth  so  wholly  different  from 
that  described  above  as  to  lead  to  a  popular  assertion  of  a  dif- 
ference of  species.  As  a  matter  of  fact,  however,  the  cones  of 
these  upland  cypresses,  when  dropping  into  the  water  be- 
low them,  reproduce  exactly  the  common  swamp  form.  The 
extraordinary  difference  in  the  aspect  of  the  tree  under  these 


508 


SOILS. 


different  conditions  is  best  seen  in  the  subjoined  diagram, 
showing  the  upland  cypress  to  assume  the  form  of  the  tall 
willow  oak,  with  which  it  is  sometimes  locally  associated. 

The  trees  from  which  the  annexed  sketch  is  taken  grew 
within  thirty  feet  of  each  other,  on  Yellow  creek,  a  small 
tributary  of  the  Tennessee  river,  in  Tishomingo  county,  Miss. 
The  soil  stratum  is  underlaid  by  a  shaly  limestone,  and  bears 
lime  vegetation. 


^fl^l 


Swamp.  Upland. 

FIG.  81. — Forms  of  Deciduous  Cypress  on  overflowed  and  on  bench-land. 

The  fact  that  the  deciduous  cypress  grows  without  difficulty 
on  the  moister  class  of  lowlands  in  California,  12  or  15  feet 
above  bottom  water,  is  of  interest  in  this  connection.  It  then 
assumes  the  upland  form  shown  in  the  figure  above,  although 
not  growing  quite  as  tall.  The  calcareous  nature  of  these  soils 
is  probably  an  important  factor  in  this  apparently  incongruous 
adaptation  of  a  subtropical  swamp  tree  to  arid  conditions.  In 
its  swamp  form  the  cypress  usually  grows  in  rather  shallow, 
heavy  clay  soil,  into  the  dense  subsoil  of  which  the  roots  pene- 
trate but  little. 


RECOGNITION  OF  CHARACTER   OF  SOILS. 


509 


Other  Lowland  Trees. — The  lowland  hickories,  like  their 
brethren  on  the  highlands,  seem  on  the  whole  to  prefer  the 
lighter  or  loamy  bottom  soils  to  those  of  a  heavier  character. 
This  is  especially  true  of  the  Pecan.  The  latter,  as  well  as  the 
shell-bark  hickory,  is  especially  indicative  of  the  highest  class 
of  bottom  soils.  The  black  walnut,  while  apparently  also  best 
suited  in  loamy  soils,  is  also  more  or  less  found  on  heavy  bot- 
tom lands,  provided  they  are  sufficiently  calcareous ;  and  the 
same  is  measurably  true  of  the  tulip  or  white-wood  tree.  The 
most  frequent  occupants  of  heavy  bottom  lands,  however,  are 
the  black  gum  and  sweet  gum,  so  that  "  gum  swamps  "  are 
usually  found  to  be  of  that  character.1  But  in  the  prairie 
region,  where  the  bottom  soils  are  very  calcareous  and  heavy, 
as  well  as  in  corresponding  soils  of  the  u  buck-shot  "  lands  of 
the  great  Mississippi  Bottom,  the  chestnut-white  (cow-  or 
basket-  )  oak  sometimes  occupies  such  ground  almost  exclu- 
sively. Among  the  accompanying  trees  are  especially  the 
honey  locust,  the  crab-apple,  mulberry  and  sweet  gum,  as  well 
as  ash. 

General  Forecasts  of  Soil  Quality  in  Forest  Lands. — While 
the  oaks  and  pines  mentioned  as  forming  the  bulk  of  the  timber 
constitute  in  the  cotton  states  the  prinia  facie  evidence,  as  it 
were,  of  the  general  character  of  the  land,  there  are  numerous 
other  trees  and  plants  which  serve  the  discriminating  land- 
seeker  as  a  guide  for  the  quality  of  the  soils  in  different  locali- 
ties. While  everywhere,  well-developed  black,  red.  Spanish 
and  white  oaks  are  considered  as  signs  of  a  high  quality  of 
land,  the  tall,  thin  scarlet,  the  upland  willow,  and  the  bar- 
rens scrub  oak  are  considered  as  indications  detracting  mate- 
rially from  the  producing  value  wherever  they  prevail.  The 
various  hickories  are  throughout  considered  as  indicating  good 
land  when  mixed  with  the  oaks,  or  by  themselves;  while  the 
presence  of  walnut,  linden  and  tulip  tree  will  usually  rai<e  the 
estimate  of  uplands  to  the  highest  class.  On  the  other  hand, 
the  occurrence  of  small  black-gum  trees  and  short-leaved  pine, 
with  low  huckleberry,  among  the  oaks  of  whatever  kind,  ac- 

1  Hence  perhaps  the  vernacular  name  "  gumbo  "  for  heavy,  adhesive  clay  soils 
in  the  north  central  states  ;  which  mav  uN<\  however,  be  derived  fr^m  a  c<>mpari 
son  with  the  "  gummy  "  pods  of  the  cultivated  okra  or  gumbo  plant. 


5io 


SOILS. 


companied  as  they  usually  are  by  the  disappearance  of  the 
black,  white  and  Spanish  oaks,  will  materially  depress  the  land- 
values. 

The  appearance  of  well-formed  oaks,  as  well  as  of  hickory, 
is  therefore  at  once  welcomed  as  an  evidence  of  soil  improve- 
ment, while  that  of  low  huckleberry  bushes  and  small  black 
gums  indicates  the  reverse.  An  increase  in  the  thickness  and 
retentiveness  of  the  soil  stratum  is  also  usually  indicated  by 
the  occurrence  of  short-leaved  pine  in  the  long-leaf-pine  areas. 

The  black,  red,  white,  and  Spanish  oaks  belong  altogether 
to  soils  of  medium  physical  constitution,  only  their  size  upon 
such  lands  depending  upon  the  relative  richness  in  plant- food ; 
but  without  such  changes  producing  any  notable  variation  in 
their  form.  Clearly  then,  these  species  are  intolerant  of  ex- 
treme physical  conditions,  and  are  practically  restricted  to  soils 
of  "  loamy  "  character  and  easy  cultivation. 


CHAPTER  XXV. 

RECOGNITION- OF  THE  CHARACTER  OF  SOILS  FROM  THEIR 

NATIVE  VEGETATION.     UNITED  STATES  AT  LARGE. 

EUROPE. 

THE  application  of  the  above  data  outside  of  Mississippi  can 
mostly  be  verified  only  in  a  fragmentary  way  from  such  data 
•as  are  casually  given  in  the  reports  of  State  Surveys,  as  well 
as  from  such  observations  as  the  writer  has  been  able  to  make 
personally  elsewhere.  In  the  latter  category  the  most  copious 
refer  to  the  states  of  Alabama.  Louisiana  and  Illinois. 

ALABAMA. — The  observations  of  Prof.  Eugene  A.  Smith, 
and  those  of  Dr.  Chas.  Mohr,  are  especially  valuable  and  cogent 
as  to  the  close  correspondence  of  the  soil  and  vegetative  phe- 
nomena with  those  observed  in  Mississippi.1  They  are  faith- 
fully reproduced  on  the  corresponding  geological  areas,  includ- 
ing also  the  Flatwoods.  Northwest  of  Mobile,  on  the  Missis- 
sippi line,  the  long-leaf-pine  forest  is  interspersed  with  more 
or  less  continuous  areas  bearing  a  fine  oak  growth,  with  hick- 
ories and  other  trees  indicating  a  calcareous  soil.  This  fea- 
ture is  most  extensively  developed  in  Alabama  in  what  is 
known  as  the  "  lime-sink  region."  on  the  borders  of  which  the 
vegetative  transition  in  passing  from  the  non-calcareous  sandy 
pine  land,  can  be  observed  in  the  most  striking  manner  and 
with  frequent  alternations.  Northward  of  the  long-leaf-pine 
licit,  the  tertiary  and  cretaceous  areas  show  in  Alabama  the 
•same  features  as  in  Mississippi,  viz..  black  calcareous  prairies 
alternating  with  ridge  lands,  among  which  in  the  cretaceous 
•area  the  Pontotoc  ridge  is  represented  by  a  series  of  isolated 
knobs,  popularly  known  as  Clninnenugga  ridge,  closely  re- 
sembling the  former  in  its  soils  and  vegetative  character. 

In  northern  Alabama,  according  to  Dr.  Smith,  on  the  vari- 
ous stages  of  the  Carboniferous  formation,  ranging  from  a 

1  See   Plant    Life  of   Alabama,  by  Charles   Mohr.    Vol.  VI.    Contr.    U.    S.   Nat. 
'Herb.,  1T.  S.  Dep't  Agr.;  Alabama  Kd.  of  Same,  Ala.  (leol.  Survey,  1901. 


512 


SOILS. 


sandy  or  conglomerate  character  to  that  of  limestones  of  vari- 
ous degrees  of  purity,  soils  contrast  strikingly  with  each  other, 
agreeing  closely  with  those  seen  in  the  neighboring  part  of 
Mississippi.  Here,  moreover,  the  contrast  between  the  natural 
vegetative  character  as  well  as  cultural  value  of  the  lands  de- 
rived from  the  magnesian  limestones  (the  "barrens")  con- 
trasts strikingly  with  those  originating  in  the  purer  limestones, 
on  which  the  blue  grass  is  at  home. 

LOUISIANA. — As  to  Louisiana,  whose  geological  formations 
correspond  closely  to  those  of  Mississippi,  it  may  be  said  in 
general  that  the  vegetative  phenomena  coincide  completely  with 
those  observed  in  Mississippi.  The  "  white-lime  country  "  of 
northeastern  Mississippi  is  represented  in  Louisiana  only  by 
patches  occurring  here  and  there  on  a  line  laid  from  Lake 
Bistineau  to  the  coast  at  Petite  Anse  Island.  But  the  chief 
characteristics  of  the  calcareous  area,  among  them  especially 
that  of  the  occurrence  of  red  cedar  and  clumps  of  crab-apple, 
persistently  reappear.  The  "  Central  Prairie  Region "  of 
Louisiana  is  quite  narrow,  but  on  it  there  reappear  precisely 
the  same  characteristics  described  in  connection  with  that  area 
in  Mississippi.  In  the  long-leaf-pine  region  of  Louisiana  there 
occur,  as  in  Mississippi,  some  isolated  patches  of  a  calcareous 
character,  the  largest  of  which  is  on  the  Bayou  Anacoco  in  Ver- 
non  Parish,  near  the  western  border  of  the  State.  As  we 
emerge  from  the  sandy  lands  of  the  long-leaf  pine  area  to  that 
underlaid  by  the  calcareous  formation,  we  find,  first,  a  change 
to  oak  and  short-leaved  pine,  then  the  oak  forest  alone ;  finally, 
on  a  level  black  prairie  of  considerable  extent,  the  post  and 
black-jack  oak  in  their  thick-set  form,  clumps  of  crab-apple,  red 
haw  and  honey  locust,  here  and  there  a  red  cedar ;  exactly  as 
has  already  been  described  in  connection  with  the  prairie  lands 
of  Mississippi.  To  southward  of  the  long-leaf-pine  area  lies  a 
broad  belt  of  level,  generally  treeless,  sandy  prairie,  in  part 
dotted  with  groves  of  timber,  but  otherwise  with  nearly  the 
same  peculiar,  small-seeded  herbaceous  vegetation  observed  in 
the  corresponding  portion  of  Mississippi.  But  in  Louisiana 
there  intervenes  between  these  gray  sour  lands  and  the  shell 
hammocks  of  the  immediate  seacoast  with  their  groves  of  live 
oak,  a  belt  of  black  calcareous  prairie,  increasing  in  width  and 
clayeyness  towards  the  West,  and  acquiring  considerable  exten- 


RECOGNITIOiN   OF  THE  CHARACTER  OF  SOILS. 


513 


sion  in  the  corresponding  portion  of  Texas.  On  these  prairies 
\ve  again  find  the  calciphile  vegetation,  including  the  honey 
locust,  clumps  of  crab  apple  and  red  haw,  etc.,  but  not  usually 
any  oak  growth,  except  (near  the  seacoast)  the  live  oak.  In 
the  hilly  country  of  northern  Louisiana  there  is  reproduced 
substantially  the  vegetative  character  of  the  "  short-leaf  pine 
and  oak  "  uplands  of  Mississippi  ( see  map  on  p.  490,  chapter 
24),  save  in  that,  owing  to  the  occasional  outcropping  of  the 
calcareous  materials  of  the  Tertiary,  small  prairies  with  black 
soil  are  spotted  about  here  and  there.  Bordering  the  Missis- 
sippi Bottom  there  are  a  series  of  oak-upland  ridges  with  a 
brown  loam  soil  corresponding  to  the  fertile  area  in  north- 
western Mississippi,  with  small  patches  of  the  "Cane  hills" 
loess  soils,  bearing  a  corresponding  tree  growth.1 

In  IVcstcrn  Tennessee  the  vegetative  zones  so  distinctly 
shown  in  the  adjacent  portion  of  Mississippi  are  not  so  strik- 
ingly outlined,  but  so  far  as  they  do  exist,  the  phenomena  ob- 
served accord  exactly  with  those  heretofore  described.  The 
same  holds  true  of  ITesfern  Kentuckv.  as  is  well  set  forth  and 
graphically  described  in  the  reports  of  the  geological  surveys 
'of  that  state  by  Dr.  David  Dale  Owen,  and  later  by  Dr.  R.  II. 
Loughridge. 

Nortli  Central  Stales.— North  of  the  Ohio  River  the  mater- 
ials of  the  geological  formations  arc  not  nearly  as  much  varied 
as  they  are  south  of  the  same;  consequently  the  vegetative 
features  are  also  much  more  uniform.  It  must  be  remembered 
that  from  the  Alleghenies  nearly  to  the  Mississippi,  the  states 
of  Ohio,  Southern  Michigan,  Indiana  and  Illinois  are  largely 
covered  by  drift  deposits  overlying  the  older  formations,  except 
that  along  the  Ohio  and  Mississippi  rivers  lies  the  calcareous 
loam  of  the  Loess  or  Bluff  formation. 

\Yithin  the  states  mentioned,  however,  not  only  are  the  older 
underlying  formations  very  generally  calcareous,  but  calcar- 
eous sand  and  gravel  form  a  large  proportion  of  the  drift  de- 
posits, which  in  most  cases  overlie  the  rocks.  Hence  we  find 
from  the  Alleghenies  to  the  Mississippi  a  predominance  of  the 
oak  forests  which  characterizes  calcareous  soils,  as  in  the  bet- 
ter class  of  uplands  in  Mississippi  and  Tennessee;  interrupted 

1  See  "  Final  Report  of  a  Geological  Reconnoisssance  of  Louisiana,"  publisher 
by  the  New  Orleans  Academy  of  Science  in  1871. 

33 


SOILS. 

only  here  and  there  by  sandy  belts  or  ridges  bearing  inferior 
growth,  among  which,  again,  the  black-jack  and  post  oaks, 
with  short-leaved  pine,  are  conspicuous.  But  in  a  large  portion 
of  Illinois,  as  well  as  in  Western  Indiana,  the  oak  forest  is  in- 
terrupted by  more  or  less  continuous  belts,  and  sometimes  by  a 
wide  expanse,  of  black  prairie,  generally  treeless  or  bearing 
only  clumps  of  crab-apple  and  haw,  and  underlaid  more  or  less 
directly  by  the  carboniferous  limestones,  \vhose  disintegration 
-has  materially  contributed  to  the  black  prairie  soils;  which  are 
noted  for  their  high  and  long-continued  productiveness.  The 
lower  ground  is  characterized,  besides  clumps  of  crab-apple 
and  red  haw,  by  the  frequent  occurrence  of  the  honey  locust, 
the  lead  plant  (Amorpha  fruticosa},  the  button-bush  (Cephal- 
anthus  occidentalis},  and  among  herbs  by  the  polar  plant 
(Silphium  laciniatum} ,  the  prairie  burdock  (S.  terebinthin- 
aceum),  the  swamp  rose-mallow  (Hibiscus  moschcutos},  the 
sneezewort  (Helenium  aiitumnalc) ,  the  wild  indigo  (Baptisia 
tinctoria  and  leucophcea). 

The  black-jack  and  post  oak  are  not  nearly  as  frequently 
found  on  the  prairies  of  Illinois  as  on  those  of  Mississippi  and 
Alabama;  but  w'here  they  occur  they  assume  a  similar  habit,  in- 
cluding the  occurrence  of  the  dwarfed,  apple-tree-shaped  form 
on  the  low  ridges  with  heavy  yellow  clay  soil,  that  sometimes 
intersect  the  prairies.  The  post  oak,  moreover,  in  a  form  quite 
similar  to  that  described  as  occurring  on  the  Flatwoods  of 
Mississippi,  forms  the  timber  of  the  "  post  oak  flats  "  occasion- 
ally found  between  the  low  ridges  bordering  the  streams,  or 
along  the  edges  of  the  prairies.  The  herbaceous  vegetation  of 
these  post  oak  flats  distinctly  characterizes  them  as  being  poor 
in  lime.  In  the  loamy  uplands,  where  the  calcareous  ingre- 
dient is  more  abundant,  the  open-headed  form  of  the  black- 
jack and  post  oak  are  also  found,  interspersed  with  a  luxu- 
riant growth  of  black,  red  and  white  oak,  with  more  or  less  of 
hickory,  which  here  assume  a  magnificent  development,  much 
superior  to  that  seen  south  of  the  Ohio.  These  yellow-loam 
uplands  correspond  very  closely  in  their  soil-composition  and 
agricultural  character  to  the  brown-loam  area  of  Mississippi 
and  Tennessee,  which  lies  inland  from  the  Loess  belt.  Where 
these  uplands  approach  the  prairie  or  the  outcrops  of  a  lime- 
stone formation,  there  is  usually  added  to  the  oak  growth  the 


RECOGNITION  OF  THE  CHARACTER  OF  SOILS.         515 

linden,  the  wild  cherry  and  the  ash ;  the  latter  two  also  usually 
appear  in  the  bottoms  of  the  streams  and  on  the  slopes  ad- 
jacent, together  with  the  walnut  and  butternut,  and  in  the 
lowest  ground  the  sycamore. 

The  tree  growth  of  the  Loess  belt  bordering  the  Ohio  and 
Mississippi,  so  far  as  climatic  differences  permit,  agrees  almost 
precisely  with  that  described  in  the  corresponding  portions  of 
Mississippi  and  Tennessee.  The  change  from  the  oak  and 
hickory  growth  covering  the  yellow-loam  uplands  toward  the 
more  calcareous  area  is  evidenced  by  the  appearance  of  large 
sturdy  trees  of  sassafras,  together  with  the  linden  and  sugar 
maple.  Descending  from  the  "  bluff  "  toward  the  rich  bottom- 
prairie  with  its  black,  heavy  soil,  we  at  once  encounter  the 
familiar  indices  of  the  more  highly  calcareous  land,  viz.,  the 
honey  locust,  clumps  of  crab  apple  and  red  haw,  with  hack- 
berry,  Kentucky  coffee  tree  and  mulberry  on  the  lower  ground  ; 
In  late  summer  and  during  autumn,  a  tall  growth  of  the  iron 
weed  (I7ernonia),  several  Eupatoriwns  (E.  pcrfoliatum  and 
pur  pur  cum,  the  white  and  the  purple  boneset)  and  of  the  blue- 
spiked  Verbena  are  very  characteristic,  as  are  also  several  spe- 
cies of  Cassia  (Carolina  coffee,  etc.,)  and  the  swamp  rose-mal- 
low. 

Upland  and  Lowland  ]*cgctation  in  tlic  Arid  and  Humid 
Regions. — In  the  humid  countries  there  is  commonly  a  marked 
difference  between  the  vegetation  of  the  uplands  and  lowlands, 
arising  not  merely  from  the  difference  in  the  moisture  supply, 
but  evidently  of  a  specific  nature.  When  we  discuss  the  char- 
acteristic plants  in  detail,  it  becomes  obvious  that  it  is  lime 
vegetation  that,  in  most  cases,  forms  the  characteristic  dif- 
ferences l>etween  upland  and  lowland  forest  growth  ;  a  nat- 
ural consequence  of  the  leach  ing-down  of  the  lime  from  the 
higher  land  to  the  lower  levels.  By  way  of  counter-proof  we 
find  that  when  the  uplands  themselves  are  of  a  calcareous 
nature,  a  part  at  least  of  the  lowland  flora  ascends  into 
them.  As  prominent  examples  may  be  mentioned  the  Tulip 
tree  (Liriodcndron),  black  walnut,  ash,  Kentucky  coffee  tree, 
Hercules'  club,  etc.,  which  are  lowland  trees  over  the  greater 
part  of  their  area  of  occurrence;  but  in  the  loess  or  Cane  hills 
bordering  the  Mississippi  and  its  larger  tributaries,  as  well  as 
in  the  limestone  regions  of  the  southwestern  and  western  states, 


516  SOILS. 

are  conspicuous  in  the  uplands  as  well.  The  tall  southern  cane 
(Arundinaria  macrosperma} ,  usually  considered  a  plant  of  the 
low  river  bottoms,  originally  covered  the  loess  or  "  Cane  hills  " 
of  the  lower  Mississippi,  with  their  highly  calcareous  soils. 
The  same  is  true  of  many  other  trees  and  shrubs  characterizing 
limy  lands.  Of  course  there  are  some  whose  habitat  is  depend- 
ent upon  the  concurrent  presence  of  both  lime  and  moisture, 
such  as  the  sycamore,  cottonwood,  hackberry,  pawpaw,  etc., 
which  are  naturally  found  only  in  stream  bottoms  or  on  low 
hammocks. 

In  the  arid  region,  on  the  contrary,  the  main  difference  in 
upland  and  lowland  vegetation  is  (outside  of  mountain  in- 
fluences) entirely  referable  to  moisture-conditions;  the  proof 
being  that  so  soon  as  the  uplands  are  irrigated  the  lowland 
flora  takes  possession.  Both  uplands  and  lowlands  being 
abundantly  calcareous,  there  then  is  no  cause  for  any  material 
differences.  This  substantial  uniformity  of  upland  and  low- 
land plant  growth  is  particularly  striking  in  the  comparatively 
restricted  floras  of  Eastern  Oregon  and  Washington,  and  in 
Montana,  where  the  more  luxuriant  growth  of  the  valleys  is  al- 
most the  only  contrast  seen  when  their  vegetation  is  compared 
with  that  of  the  uplands  adjacent. 

Forms  of  Deciduous  Trees  in  the  Arid  Regions. — Since,  as 
shown  above,  the  soils  of  the  arid  regions  are  almost  through- 
out calcareous,  we  should  expect  that  the  forms  of  the  native 
trees  would  in  general  conform  to  the  rule  given  above.  As 
regards  the  deciduous  trees  this  is  very  generally  true :  We 
rarely  see  on  the  Pacific  slope,  south  of  Oregon,  anything  to 
compare  with  the  tall  oaks  of  the  Atlantic  forests.  The  native 
oaks  are  as  a  rule  of  low,  spreading  growth,  with  stout,  short 
trunks;  and  as  they  rarely  form  dense  forests,  the  timbered 
areas  have  an  orchard-like  appearance,  characteristic  of  the 
landscapes  of  the  arid  region,  from  the  Mezquit  Plains  of 
Texas  to  Eastern  Oregon  and  Washington.  Only  where  a 
very  abundant  supply  of  moisture  prevails  do  we  find  occa- 
sional exceptions.  The  trees  of  the  humid  region  when  trans- 
planted to  California  have  a  perverse  tendency  to  branch  low, 
so  that  only  the  most  persistent  trimming-up  will  induce  them 
to  form  trunks  at  all  like  those  found  in  their  native  climes.  In 


RECOGNITION  OF  THE  CHARACTER  OF  SOILS. 


517 


some  cases  no  amount  of  trimming  will  result  in  the  formation 
of  anything  more  than  bushes. 

It  may  be  objected  that  the  arid  climate  as  such,  and  not  the 
calcareous  nature  of  the  soil,  is  the  cause  of  this  tendency.  It 
is  unquestionable  that  this  low-branching  habit  is  a  distinct 
advantage  to  the  plants,  whose  trunks  would  otherwise  be  fre- 
quently scorched  by  the  hot  summer  sun ;  as  happens  when 
Eastern  settlers  try  to  grow  "  standard  "  fruit  trees,  with  the 
result  that  a  "  sore,"  or  sunburnt  streak  is  formed  on  the  south- 
west side  of  the  exposed  trunk.  All  orchard  trees  should 
therefore  be  pruned  "  vase-shape  "  in  arid  climates,  partly  for 
this,  partly  for  other  reasons.  But  this  cannot  explain  the 
fact  that  seedlings  from  eastern  acorns  act  precisely  as  do  accli- 
mated trees;  so  that  it  is  not  a  case  of  the  survival  of  the 
fittest  to  endure  arid  conditions. 

Tall  Growths  of  Conifers.  Moreover,  while  the  rule  holds 
good  with  almost  all  deciduous  trees,  it  is  not  applicable  to  the 
Conifers;  which  in  the  case  of  the  Sequoias  (redwoods  and 
"big-trees"),  sugar  pine  and  others,  exemplify  some  of  the 
tallest  growths  known  in  the  world.  The  Eastern  Cedar  or 
Juniper  grows  tall  only  on  sufficiently  calcareous  soils,  and  in 
the  Mississippi  Valley  states  at  least,  wherever  it  occurs  is  an 
unfailing  indication  of  calcareous  lands.  The  extended  oc- 
currence of  the  spruce  on  the  Allegheny  Ranges,  where  lime- 
stone formations  prevail  so  largely,  seems  to  indicate  a  similar 
preference  for  calcareous  lands.  And  this  is  certainly  true  of 
the  black  locust,  which  reaches  its  extreme  southern  range  in 
the  cretaceous  hills  of  Northeastern  Mississippi,  showing  the 
stout,  stocky  form  it  also  assumes  when  planted  in  the  calcare- 
ous black-prairie  lands  of  Illinois. 

Herbaceous  Plants  as  Soil  Indicators.  \Yhi1c  herbaceous 
plants  are  not  as  generally  considered  by  land-seekers  in  judg- 
ing of  soil  fertility  and  character,  it  goes  without  saying  that 
very  many  are  quite  as  characteristic  as  the  tree  vegetation, 
especially  when  deep-rooting,  so  as  not  to  indicate  merely  the 
character  of  a  few  inches  of  surface  soil. 

In  the  Middle  West  of  the  I'nitcd  States  especially,  a  large 
number  of  the  Composite  serve  as  marks  of  high  productive 
capacity.  This  is  particularly  true  of  the  larger  species  of 
the  sunflower  tribe,  among  which  Hclianthus  grossc-scrratus 


5i8  SOILS. 

and  doronicoides  are  perhaps  the  most  generally  notable ;  while 
farther  west,  beginning  with  Kansas,  the  "  Sunflower  State," 
and  its  northern  neighbor,  H.  annuus,  whether  native  or  intro- 
duced, becomes  conspicuous  also.  The  Silphiums  (compass 
sunflowers)  have  nearly  the  same  significance,  S.  laciniatum 
and  perfoliatutn  being  prominent  on  the  prairies  of  Illinois  and 
Indiana ;  but  in  land  under  cultivation  they  are  mostly  re- 
placed by  a  luxuriant  growth  of  the  Ragweed,  Ambrosia  tri- 
fida.  Various  species  of  Bidens  (beggar  ticks),  notably  the 
B.  aristata  and  cernua,  accompany  the  true  sunflowers  in  the 
lower  grounds  of  these  regions,  as  do  also  Heliopsis  laevis, 
Coreopsis  triperis  and  Rudbeckia  (Obeliscaria)  pinnata. 
Rudbeckia  hirta  and  purpurea,  though  also  occurring  on  rich 
soils,  are  not  characteristic  of  them.  The  larger  species  of 
golden  rods  (Solidago),  notably  ,S\  canadensis,  rigida  and 
speciosa  (not  ordinarily  distinguished  by  farmers)  share 
substantially  the  distribution  of  the  large  sunflowers  men- 
tioned above.  Of  the  Asters,  only  A.  novcc-anglicc  serves  as 
a  reliable  guide  to  high-class  lands  in  the  Middle  West,1  but 
a  very  copious  growth  of  asters  and  solidago  of  various  species 
is  always  a  welcome  indication  of  land  quality,  and  indicates 
soils  of  good  lime  content,  if  not  absolutely  calcareous. 

Leguminous  Plants. — It  is  generally  understood  that  most 
leguminous  plants,  and  among  them  especially  the  clovers,  in- 
dicate rich,  or  rather,  calcareous  lands.  The  very  large  pro- 
portion of  lime  contained  in  the  ash  of  legumes  at  once  creates 
this  presumption,  which  is  fully  confirmed  by  experience  so  far 
as  our  ordinary  culture  plants  of  that  relationship  are  con- 
cerned. The  favoring  effect  of  lime  on  the  development  of 
bacteria,  so  essential  to  the  full  development  of  cultivated 
legumes,  has  already  been  referred  to.  The  favoring  effect  of 
gypsum  sown  even  in  small  amounts  with  clover  and  other 
legumes,  may  probably  be  referable  to  the  known  action  of  that 
salt  in  promoting  nitrification,  which  in  the  first  stages  of 
leguminous  growth  is  so  highly  favorable  to  a  vigorous  and 
early  start  of  the  crop,  and  to  a  more  copious  production  of  the 
nitrogen-assimilating  nodules.  The  quick  change  noted  in 
meadows  and  pastures  of  languishing  production  so  soon  as 
moderately  limed,  by  the  appearance  of  clover  among  the  herb- 

1  In  view  of  its  specific  designation  and  the  reputed  poverty  of  New  England 
soils,  this  is  rather  unexpected. 


RECOGNITION  OF  THE  CHARACTER  OF  SOILS.          519 

age,  at  once  reminds  us  that  the  Rhizobia  do  not  flourish  in 
acid  lands.  The  great  prevalence  of  leguminous  plants  of  all 
kinds  in  the  arid  region — clovers  (not  fewer  than  twenty-three 
species  in  California  alone),  Lupins,  Astragalus  and  related 
genera,  at  once  remind  us  of  the  universal  prevalence  of 
calcareous  soils  in  these  regions,  as  shown  above.  Mutatis 
mutandis,  we  find  precisely  the  same  general  facts  in  the  arid 
regions  of  the  other  continents. 

Nevertheless,  it  must  be  kept  in  mind  that  not  all  plants  of 
the  leguminous  order  are  positively  "  calciphile."  Within  the 
United  States,  it  is  especially  the  genera  Desmodium  (Mei- 
bomia]  and  Lespcdcza,  which  are  very  numerously  represented 
in  the  long-leaf  pine  region  of  Mississippi,  where  the  soils  are 
so  poor  in  lime.  Whether  under  these  conditions  these  plants 
develop  the  rhizobian  nodules,  has  not,  so  far  as  the  writer 
is  aware,  been  definitely  observed.  Certain  it  is  that  quite 
a  number  of  these  plants  occur  on  both  calcareous  and  non- 
calcareous  soils,  and  on  the  latter  assume  a  much  more  vigor- 
ous development  than  in  the  pine  woods.  But  it  is  evident  that 
they,  with  a  few  others  (c.  g.  Galactia  moll  is,  Cassia  chamcc- 
crista  and  nictitans)  are  more  or  less  indifferent  to  the  lime- 
content  of  soils,  and  cannot  therefore  be  relied  upon  in  judg- 
ing the  quality  of  lands.  In  Mississippi  and  northern  Ala- 
bama, the  Tcphrosia  virginica  ("  devil's  shoestring"),  associ- 
ated with  chestnut  and  short-leaved  pine,  is  characteristic  of 
the  poorest  non-calcareous  lands,  and  bears  seeds  but  very 
scantily.  It  disappears  so  soon  as  calcareous  lands  are  ap- 
proached, together  with  the  chestnut  tree. 

EUROPEAN  OBSERVATIONS  AND  VIEWS  ON   PLANT  DISTRIBUTION 
AND  ITS  CONTROLLING  CAUSES. 

The  writer  has  thus  far  presented  and  discussed  mainly  his 
own  observations  made  in  the  United  States,  without  refer- 
ence to  the  previous  and  contemporaneous  work  on  the  same 
subject  in  Kurope.  There  arose  certain  discrepancies  which 
could  not  well  be  explained  without  a  previous  full  consider- 
ation of  American  conditions. 

As  is  well  known,  for  nearly  twenty  years  the  accepted 
theory  in  Kurope  was  that  of  Thurman.1  which  attributes  the 

1  Essai  de  Fhytostatique  appliquce  a  la  chaine  du  Jura  et  aux  contrccs  voisines, 
2  vols.  Svo.  Herne,  1849. 


320  SOILS. 

liable  to  be  washed  or  leached  out  of  the  soil  by  heavy  rains 
or  irrigation,  and  would  be  lost  in  the  country  drainage.  It 
is  therefore  clearly  desirable  that  only  a  relatively  small  pro- 
portion of  the  useful  soil-ingredients  should  be  in  the  water- 
soluble  or  physically  absorbed  condition,  but  that  a  larger  sup- 
ply should  be  present  in  forms  not  so  easily  soluble,  yet  ac- 
cessible to  the  solvent  action  which  the  acids  of  the  soil  and  of 
the  roots  of  plants  are  capable  of  exercising.  This  "virtually 
available  supply  we  may  designate  as  the  reserve  food-store. 
Finally,  there  is  practically  in  all  soils  a  certain  proportion 
of  the  soil-minerals  in  their  original  form,  as  they  existed  in 
the  rock-materials  from  which  the  soil  was  formed.  These 
minerals  being  usually  in  a  more  or  less  finely  divided  or  pul- 
verulent condition,  they  are  attacked  much  more  rapidly  by 
the  chemically-acting  "  weathering "  agencies,  viz.,  water, 
oxygen,  carbonic  and  humus  acids,  than  when  in  solid  masses ; 
and  thus,  transformation  of  the  inert  rock-powder  into  the 
other  two  classes  of  mineral  soil-ingredients  progresses  in 
naturally  fertile  soils  with  sufficient  rapidity  to  produce,  in  a 
single  season,  sensible  and  practically  important  results,  known 
as  the  effects  of  fallowing. 

The  Reserve. — The  nature  of  these  processes  has  been  dis- 
cussed in  chapters  I  to  4;  and  it  will  be  remembered  that  two 
of  their  most  prominent  results  are  the  formation  of  clay,  and 
of  zeolitic-compounds,  the  latter  being,  as  heretofore  stated 
(pp.  36  ff)  hydrous  silicates  of  earths  and  alkalies,  easily  de- 
composable by  acids,  and  also  capable  of  exchanging  part  or 
the  whole  of  such  basic  ingredients  with  solutions  of  others 
that  may  enter  the  soil.  These  zeolitic  compounds  therefore 
fulfil  two  important  functions  in  the  premises,  viz. :  a  ready 
yielding-up  of  part  of  their  ingredients  to  acid  solvents,  and 
a  tendency  to  fix,  by  exchange,  a  portion  or  the  whole  of  the 
soluble  compounds  that  may  be  set  free  in,  or  brought  upon 
the  land.  The  first-mentioned  property  is  of  direct  avail  in 
that  the  soil-humus  forms,  and  the  roots  of  plants  exude,  acid 
solvents  on  their  surface,  and  can  thus  draw  upon  the  reserve 
store  of  food;  the  second  tells  in  the  direction  of  preventing 
the  waste  of  water-soluble  manurial  ingredients  supplied  to, 
or  formed  in  the  soil.  (See  above,  chapter  3,  page  38). 


THE  PHYSICO-CHEMICAL  INVESTIGATION  OF  SOILS. 


321 


The  reserve  food-store  may  then  be  placed  under  the  fol- 
lowing heads : 

Hydrous  or  "  zcolitic "  silicates,  from  which  dilute  acids 
can  take  up  the  bases  potash,  soda,  lime  and  magnesia.  These 
silicates  may  be  in  either  the  gelatinous  or  powdery  form ;  in 
the  former  case  they  may  also  occlude  water-soluble  sub- 
stances. 

Carbonates  of  lime  and  magnesia,  which  are  readily  dis- 
solved by  carbonated  water  as  well  as  by  the  vegetable  acids. 

Phosphates  of  lime  and  magnesia,  not  very  readily  soluble 
in  carbonated  water,  but  more  readily  attacked  by  the  acids 
of  the  soil  and  of  plant  roots;  thus  supplying  phosphoric  acid 
to  plants.  The  more  finely  divided  they  are  the  more  readily 
they  are  dissolved ;  some  soils  containing  only  crystalline 
needles  of  apatite  (see  chap.  5,  p.  63)  only  are  nevertheless 
poor  in  available  phosphoric  acid. 

The  natural  phosphates  of  iron  and  alumina  are  practically 
insoluble  in  all  solvents  at  the  disposal  of  vegetation  and 
though  present  in  considerable  amounts  in  some  soils,  (see 
chapter  19.  page  355),  may  be  considered  as  being  permanently 
inert,  and  therefore  not  to  be  counted  among  the  soil  resources 
for  plant  nutrition.  As  yet  no  artificial  process  by  which 
their  phosphoric  acid  can  be  made  available  within  the  soil, 
has  been  discovered. 

U'ater-soluble  Ingredients. — As  regards  these  it  has  already 
been  explained  that  they  are  largely  retained  in  the  condition 
of  purely  physical  adsorption,  as  in  the  case  of  charcoal  or 
quartz  sand,  through  which  sea  water  filters  and  is  thereby 
partially  deprived  of  its  salts.  But  these  can  be  gradually 
withdrawn  by  washing  with  pure  water  alone,  and  still  more 
easily  when  stronger  solvents  are  used.  Since  the  soil-water 
is  always  more  or  less  charged  with  carbonic  acid,  and  the 
roots  themselves  secrete  carbonic  as  well  as  stronger  acids  in 
their  absorption  of  mineral  plant-food,  there  is  no  difficulty 
about  explaining  the  manner  in  which  such  physically  con- 
densed ingredients  are  taken  up.1 

1  Whitney  (Hull.  22,  U.  S.  Bureau  of  Soils)  claims  on  the  basis  of  a  large  number 

of  (three-minute)  extractions  of  soils  made  with  distilled  water,  that  those  solutions 

are  essentially  of  the  same  composition  in  all  soils;   that  all  soils  contain   enough 

plant-food  to  produce  crops  indefinitely ;  and   that  the  differences    in   production 

21 


522  SOILS. 

only  a  purely  physical  action.  That  potash,  phosphoric,  acid 
and  nitrogen,  while  most  essential  as  plant-foods,  exert  other- 
wise little  if  any  effect  on  general  plant-distribution.  He  al- 
ludes similarly  to  magnesia;  and  his  final  conclusion  is  that 
"  chemical  are  in  general  more  potent  than  physical  influences," 
and  that  the  most  widely  active  influences  are  carbonate  of 
lime  and  chlorid  of  sodium.  He  does  not,  of  course,  deny  the 
potent  influence  of  moisture  upon  plant  distribution. 

Since  these  publications  were  made,  many  observers  have 
investigated  the  subject,  and  the  broad  distinction  between 
lime-loving  or  calciphile  and  lime-repelled  or  calcifuge  plants 
has  been  very  generally  recognized  and  discussed :  but  the 
cause  of  this  discrimination  by  plants  is  still  more  or  less  the 
subject  of  controversy.  Some  still  claim  that  the  calcifuge 
plants  (such  as  the  chestnut,  the  huckleberries  and  whortle- 
berries, the  heather  and  many  other  Ericaceae,  most  sedges, 
etc.)  are  repelled  by  calcareous  lands  because  they  need  a  large 
supply  of  silica,  which  they  suppose  cannot  well  be  assimilated 
in  presence  of  much  lime;  hence  they  also  designate  the  calci- 
fuge plants  as  "  silicophile  " ;  while  others  attribute  the  prefer- 
ence of  calciphile  plants  to  the  physical  effects  produced  upon 
the  soil  by  lime,  as  outlined  above  (chapter  20,  page  379). 

The  contention  that  the  presence  of  much  lime  in  soils  ren- 
ders silica  insoluble  and  hence  unassimilable  by  plants,  is  at 
once  negatived  by  the  fact  that  waters  exceptionally  rich  in 
silica,  partly  simply  dissolved  by  carbonic  acid,  partly  in  the 
form  of  water-soluble  alkali-silicates,  are  very  abundantly 
found  in  the  arid  region.  This  is  especially  the  case  in  Cali- 
fornia, where  moreover  a  number  of  species  of  very  rough- 
surfaced  horsetail  rushes  and  grasses  prove  the  ready  absorp- 
tion of  silica  when  wanted,  even  in  strongly  calcareous  soils. 
But  the  question  is  whether  the  supposed  class  of  silicophile 
plants  is  a  reality  or  merely  a  theoretical  fiction,  based  upon 
the  habit  of  speaking  of  "  siliceous  "  soils  as  a  class  apart  from 
other  and  especially  heavier  or  clay  soils.  As  a  matter  of  fact, 
the  siliceous  soils  usually  so  called  are  simply  those  poor  in  clay 
and  lime — in  other  words,  "  light  "  lands,  the  outcome  of  the 
weathering  of  quartzose  rocks  into  sandy  soils,  which  in  the 
humid  region  are  always  poor  in  lime  because  thoroughly 
leached.  In  the  arid  region,  on  the  contrary,  sandy  lands  are 


RECOGNITION  OF  THE  CHARACTER  OF  SOILS. 


523 


quite  commonly  just  as  calcareous  as  the  heavier  soils,  and 
show  no  "  silicophile  "  flora. 

According  to  the  writer's  observations  and  views,  it  being 
obvious  that  some  plants  are  practically  indifferent  to  the  pres- 
ence or  absence  of  lime  in  the  soil  except  in  so  far  as  it  influ- 
ences favorably  the  physical  conditions,  moisture  must  always 
stand  first  as  the  condition  of  maximum  crop  production,  and 
as  a  conditio  sine  qua  non  of  the  best  development  of  plants  on 
all  kinds  of  soils ;  its  best  measure  being  a  matter  of  special 
adaptation  to  each  species.  But  this  being  understood,  he 
agrees  with  Contejean  as  to  the  commanding  influence  of  lime 
in  determining  the  adaptation  of  soils  to  plants,  both  cultivated 
and  wild.  At  the  same  time,  it  is  obvious  that  the  absence  of 
the  opportunity  to  observe  really  native  vegetation,  adapted  to 
the  soils  through  ages,  has  created  for  European  observers 
difficulties  which  are  readily  solved  where  original  native 
floras  are  available. 

Schimper  1  says  pointedly  that  observations  prove  that  the 
differences  between  the  location  of  plants  on  calcareous  and 
siliceous  soils  are  not  constant,  but  vary  from  province  to 
province;  that  c.  g.,  the  list  of  indifferent  (bodensteter)  plants 
for  the  Alps  do  not  hold  good  in  the  Dauphine,  still  less  be- 
tween the  Carpathians  and  Skandinavia.  According  to 
Wahlenberg  the  following  species  are  calciphile  in  the  Carpath- 
ians, and  according  to  Christ  indifferent  in  Switzerland : 
Dryas  octopctala,  Saxifrciga  oppositifolia,  most  of  the  legumin- 
ous species,  Gentiana  nh'alis,  G.  tcnclla,  G.  I'crna,  Erica  carnca, 
Chamccorchis  alpina,  Care.r  capillaris.  Gcum  rcptans  is  re- 
ported by  Bonnier  to  be  exclusively  calciphile  on  Mont  Blanc, 
exclusively  silicophile  in  the  Dauphine;  indifferent  in  Switzer- 
land. A  great  number  of  similar  contradictions  are  reported 
by  others  as  well,  and  the  entire  subject  thus  becomes  rather 
vague;  so  that  Schimper  and  others  suggest  that  climatic  con- 
ditions may  in  part  be  responsible  for  these  discrepancies. 

In  all,  or  nearly  all  these  cases,  it  is  tacitly  assumed  that  the 
underlying  geological  formation  has  essentially  been  the  source 
of  the  soil,  and  that  its  character  is  determined  accordingly. 
But  this  assumption  is  wholly  arbitrary  unless  confirmed 
by  actual  direct  examination.  A  soil-formation  overlying 

1  Pflanzengeographie.  p.  1 1 1  &  ff. 


524  SOILS. 

limestone  on  the  slopes  of  a  range  may  be  wholly  derived  from 
non-calcareous  formations  lying  at  a  higher  elevation,  or  may 
have  been  leached  of  its  original  lime-content  by  abundant 
rains.  The  feldspars  constituting  rocks  designated  as  granite, 
may  or  may  not  be  partially  or  wholly  of  the  soda-lime  in- 
stead of  the  potash  series ;  the  mica  may  or  may  not  be  partially 
replaced  by  hornblende,  in  which  cases  the  soil  would  be  cal- 
careous to  the  extent  of  determining  the  character  of  the  flora 
as  calcifuge  or  calciphile,  without  its  being  at  all  evident  in  the 
physical  character  of  the  soil,  which  would  still  be  "  granitic  " 
or  "  siliceous."  Such  observations  in  order  to  be  critically 
decisive,  clearly  require  that  the  observer  should  be,  not  merely 
a  systematic  botanist,  nor  a  mere  geologist  or  chemist,  but  all 
these  combined.  There  is  good  reason  to  believe  that  most  or 
all  of  these  supposed  contradictions  would  disappear  before  a 
critical  physical  and  chemical  examination  of  both  the  soils  and 
the  rocks  from  which  they  are  supposed  to  have  been  derived. 
Contejean  himself,  in  placing  so  many  of  his  long  catalogue  of 
plants  into  the  doubtful  groups,  suggests  many  cases  in  which 
the  above  considerations  may  explain  the  apparent  dis- 
crepancies. 

What  is  a  calcareous  soil?  The  definition  adopted  for  this 
volume  has  been  given  in  a  previous  chapter  (chapter  19,  page 
367)  ;  viz,  that  a  soil  must  be  considered  calcareous  so  soon  as 
it  naturally  supports  a  calciphile  flora — the  "  lime  vegetation  " 
so  often  referred  to  above  and  named  in  detail.  Upon  this 
basis  it  has  been  seen  that  some  (sandy)  soils  containing  only 
a  little  over  one-tenth  of  one  per  cent,  of  lime  show  all  the 
characters  and  advantages  of  calcareous  soils ;  while  in  the  case 
of  heavy  clay  soils,  as  has  been  shown,  the  lime-percentage 
must  rise  to  over  one-half  per  cent,  to  produce  native  lime 
growth.  While  in  the  United  States  observations  of  the  con- 
trasts between  calciphile  and  calcifuge  floras  are  easily  made 
in  the  field,  and  the  facts  must  attract  the  attention  of  any 
fairly  qualified  observer,  in  Europe  they  would  have  to  be  made 
the  subject  of  special  cultural  investigation  based  upon  soil 
analysis ;  a  procedure  not  yet  fully  accredited  abroad,  any  more 
than  in  the  United  States.  In  a  general  way  it  has  however 
been  recognized  by  Msercker,  as  shown  at  the  end  of  the  pre- 
ceding chapter.  How  far  this  estimate  was  based  upon  Ameri- 


RECOGNITION   OF  THE  CHARACTER  OF  SOILS. 


525 


can  precedents,  can  now  be  only  conjectured.  Certain  it  is 
that  the  European  definition  of  calcareous  soils  remains  to  the 
present  day  a  wholly  different  one  from  that  stated  above; 
and  from  this  have  arisen  the  greater  part  of  the  doubts  and 
differences  of  opinions  among  European  botanists  as  to  the 
classification  of  plants  in  relation  to  calcareous  soils.  Two 
per  cent,  of  lime  (equivalent  to  nearly  double  the  amount  of 
carbonate)  is  the  prevailing  European  postulate  for  a  cal- 
careous soil.  Some  go  so  far  as  to  postulate  effervescence 
with  acids,  requiring  about  5/0  of  the  carbonate. 

Predominance  of  Calcareous  Formations  in  Europe. — It 
is  not  generally  recognized  even  among  geologists  how 
abnormally  predominant  are  limestone  formations  in  Europe. 
In  all  works  on  European  agriculture  we  find  the  "  lime 
sand  "  mentioned  as  a  normal  ingredient  of  soils,  specially 
provided  for  (or  against)  in  the  operations  of  soil  exami- 
nation. Its  presence  is  the  rule,  its  absence  the  exception. 
Soils  as  poor  in  lime  as  are  those  of  the  long-leaf  and  short- 
leaf  pine  regions  of  the  United  States,  are  there  very  excep- 
tional and  ( like  the  "  Haideboden  "  of  northern  Germany) 
have  long  remained  almost  uncultivated.  Calcareous  soils 
being  the  rule  in  the  regions  of  intense  culture,  the  ideas 
of  both  agriculturists  and  agricultural  chemists  have  in 
Europe,  in  the  main,  been  based  upon  them  as  normal  soils; 
so  that  instead  of  comparing  calcareous,  and  non-calcareous 
soils  properly  speaking — /.  e.,  such  as  would  not  bear  native 
lime-vegetation — the  majority  of  comparisons  has  actually 
been  made  between  soils  which,  in  the  American  sense,  were 
all  or  chiefly  within  the  calcareous  class.  It  is  characteristic 
of  this  state  of  things  that  the  injuriousness  of  an  e.vccss  of 
lime  is  among  the  foremost  themes  of  European  (especially 
French  and  English  )  agricultural  writers,  as  against  the  bene- 
ficent effects  prominently  assigned  to  lime  in  America.  Xo 
such  popular  saying  as  that  "a  lime  country  is  a  rich  coun- 
try" exists  in  Europe;  on  the  contrary,  we  constantly  hear, 
and  see  in  books,  the  mention  of  "  poor  chalk  lands."  and  in 
France  especially  the  deleterious  effects  of  excess  of  lime  upon 
crops  is  the  theme  of  remark.  Excess  of  lime  in  their  marly 
lands  has  been  the  despair  of  French  vintners,  and  Yiala  was 
specially  sent  to  America  to  find  some  vine  to  serve  as  a 


526  SOILS. 

grafting  stock  which  would  resist  the  tendency  to  chlorosis 
which  renders  many  of  the  American  phylloxera-resistant 
vines  useless  to  the  viticulturists  of  France.  Viala  did  not 
find  such  grape-vines  until  he  reached  the  cretaceous  (chalk) 
area  of  Texas,  where  the  native  vines  had  long  ago  adapted 
themselves  to  marly  soils;  and  these  vines  have  solved  the 
problem  for  French  viticulture. 

And  England,  France,  Belgium  and  most  of  western 
Europe  are  rich  countries,  largely  owing  to  their  abundant 
limestone  formations;  and  it  may  be  questioned  whether,  had 
this  been  otherwise,  Europe  would  so  long  have  remained  the 
center  of  civilization ;  for  starving  populations  are  not  a  good 
substratum  for  high  mental  culture  and  progress.  It  may 
equally  be  asked  whether  the  invariably  calcareous  character 
of  arid  soils,  as  heretofore  shown,  has  not,  together  with 
their  general  high  quality,  been  largely  a  determining  factor 
in  the  location  and  persistence  of  so  many  ancient  civilizations 
in  arid  lands;  as  outlined  in  chapter  21,  page  417.  In  this  con- 
nection, the  proper  distinction  between  calcareous  and  non- 
calcareous  soils  passes  from  the  domain  of  natural  science  to 
that  of  the  history  of  human  civilization. 


CHAPTER  XXVI. 

THE  VEGETATION   OF  SALINE  AND  ALKALI  LANDS. 

Marine  Saline  Lands. — While  the  saline  alluvial  lands  of 
the  sea-coast  differ  both  in  their  mode  of  origin  and  in  their 
nature  from  the  alkali  soils  or  "  terrestrial  saline  lands,"  as 
they  have  been  called  in  Europe,  their  vegetation  has  in  many 
respects  a  common  character.  Not  only  is  there  much  simi- 
larity, sometimes  even  identity,  in  the  kinds  of  plants  inhab- 
iting these  lands,  but  their  saline  ingredients  induce  certain 
changes  of  form  and  structure  in  plants  not  properly  "  saline  " 
but  more  or  less  tolerant  of  soluble  salts,  by  which  the  saline 
or  alkali  character  of  the  lands  may  be  recognized. 

Just  as  in  the  case  of  lime  \ve  must  distinguish  between  the 
plants  definitely  repelled  by  a  large  amount  of  this  substance 
in  the  soil  (calcifuge),  while  others  prefer  the  soils  in  which 
lime  is  abundant  (calciphile) ,  and  still  others  appear  to  be  in- 
different to  its  presence  and  are  governed  in  their  habitat 
by  the  physical  conditions  presented :  so  in  the  case  of  saline 
lands  the  salts  may  attract  or  repel  certain  plants.  The  lat- 
ter class  is  much  the  largest ;  while  there  is  also  a  number  of 
plants  which  are  more  or  less  indifferent  to  the  presence  of 
salts,  provided  these  be  not  in  very  great  excess.  Such  plants 
constitute  the  next-largest  class;  while  those  attracted  by  salts, 
and  whose  welfare  is  conditioned  upon  their  presence,  are 
comparatively  few  in  number,  and  still  fewer  among  them  are 
of  economic  importance.  Hence  the  soluble  salts  have  largely 
a  negative  importance  for  agriculture;  the  question  usually 
being  how  to  utilize  the  land  until  the  undesirable  surplus  of 
salts  can  be  got  rid  of,  partially  or  wholly,  as  the  case  may  be; 
the  former  usually  in  sea-shore  lands,  the  latter  in  the  alkali 
lands  proper;  in  which  a  small  remnant,  not  sufficient  to  injure 
crop  plants,  is  usually  desirable  (see  chapt.  23.  p.  462). 

General  Character  of  Saline  ]\"gctation. — Those  familiar 
with  seashore  marshes  cannot  fail  to  note  the  tleshincss  and 

527 


528  SOILS. 

succulence  of  the  characteristic  plants.  This  "  incrassation  " 
belongs  not  only  to  the  saline  flora  proper,  but  is  acquired  to  a 
greater  or  less  degree  when  plants  not  ordinarily  at  home  on 
saline  ground  are  transferred  to  it  artificially,  or  by  saline 
overflows;  while  at  the  same  time  the  leaves  usually  become 
smaller,  and  the  growth  more  compact.  Correspondingly, 
when  saline  plants  are  transferred  to  non-saline  ground,  the 
leaves  generally  become  thinner  and  larger,  and  the  growth 
more  slender.  The  well-known  "  Russian  thistle  "  is  a  case 
in  point,  as  is  also  its  close  relative,  the  soda  saltwort  (Sal- 
sola  soda)  ;  although  the  latter  does  not  often  venture  as  far 
from  the  saline  lands  as  does  the  former  (Salsola  kali  tragus), 
which  now  seems  to  have  become  a  world-wide  weed,  with 
only  a  shade  of  preference  for  alkali  lands. 

Structural  and  Functional  Differences  Caused  by  Saline 
Solutions. — It  has  been  definitely  shown  by  the  investigations 
of  Schimper,  Brick,  Hoffmann,  Lesage,  Rosenberg  and 
others,  that  the  peculiarities  or  changes  of  structure  brought 
about  by  saline  solutions  are  essentially  those  pertaining  to 
xerophile  (drought-enduring)  vegetation;  which  in  general 
tend  to  the  diminution  of  evaporation  from  the  plant  surfaces. 
It  may  be  said,  roughly  speaking,  that  the  absorption  of  water 
by  the  roots  begins  to  diminish  so  soon  as  the  concentration 
of  the  saline  solution  approaches  or  exceeds  one-half  of  one 
per  cent;  while  when  it  rises  as  high  as  three  per  cent.,  water- 
absorption  by  the  roots  ceases  even  in  the  wettest  soils,  and  the 
plant  suffers  from  drought  quite  as  much  as  from  any  di- 
rectly injurious  effects  of  the  salts.  Different  plants  of 
course  differ  in  the  measure  of  concentration  which  brings 
about  these  phenomena,  which  vary  also  with  the  character  of 
the  soluble  salts.  It  is  stated  that  injurious  or  useless  salts 
like  common  salt  act  at  lower  concentrations  than  e.  g.,  salt- 
peter, which  is  useful.  The  difference  in  external  structure 
are :  diminution  of  the  size  of  leaves,  assumption  of  cylindrical 
or  spinous  forms,  sinking-in  of  the  breathing  pores  below  the 
outer  surface,  dense  hairy  covering,  resinous  exudations,  etc. 
Internally  we  find  that  xerophile  plants  have  developed  on 
their  upper  or  outer  leaf-surfaces  instead  of  one,  several  lay- 
ers of  "palisade"  (long  and  erect,  closely-packed)  cells, 
through  which  transpiration  is  extremely  slow,  as  is  also  the 


SALINE  AND  ALKALI  LANDS. 


529 


transmission  of  heat.  When  salt-tolerant  plants  are  grown  on 
saline  soils,  their  palisade  cells  are  relatively  lengthened. 

Coincident  with  these  external  means  for  the  retardation 
of  evaporation,  the  leaves  of  xerophiles  are  frequently  sup- 
plied with  special  water-storage  cells,  which  supply  moisture 
for  the  physiological  processes  when  the  root  supply  falls 
short.  The  cactus  trihe  and  similar-looking  plants  are  ex- 
amples of  the  latter  provision,  which  causes  even  animals 
suffering  from  thirst  to  resort  to  them,  although  they  eschew 
the  saline  vegetation. 

Absorption  of  the  Salts. — The  true  halophytes  or  exclusive 
salt  plants,  which  refuse  to  grow  on  lands  not  containing  a 
large  proportions  of  salt,  often  absorb  so  much  salt  that  on 
drying  it  blooms  out  on  their  surface;  they  usually  have,  even 
when  green,  a  distinctly  salty  taste,  and  their  ash  is  rich  in 
chlorids,  specially  of  sodium.  Such  is  the  case  of  the 
samphire,  common  in  saline  marshes  everywhere.  The  total 
ash  is  usually  very  high,  often  varying  with  the  salinity  of 
the  water  or  soil  in  which  they  have  grown.  Thus  the  salt- 
content  of  the  ash  of  samphire  may  vary  by  several  per  cent. 
In  other  cases,  as  in  that  of  one  of  the  Australian  saltbushes 
investigated  at  the  California  station,  neither  the  ash  content 
nor  the  composition  of  the  ash  varies  materially  whether  the 
plant  be  grown  on  strong  alkali  land,  or  on  uplands  whose 
total  saline  content  does  not  exceed  (in  four  feet  depth) 
.015' r  or  2500  pounds  per  acre. 

The  following  table  gives  the  composition  of  the  ash  of 
this  saltbush  alongside  of  that  of  two  other  prominent  alkali- 
plants  of  the  same  relationship,  occurring,  one  in  the  San 
Joaquin  valley  of  California,  in  strongly  saline  lands,  the 
other  in  the  (treat  1'asin  region  of  the  interior,  on  lands 
strongly  impregnated  with  carlxmate  of  soda.  All  these,  it 
will  be  seen,  take  up  very  large  amounts  of  sodium  salts. 
notably  the  chlorid  ;  the  Australian  plant  most  so.  the  "  grease- 
wood  "  of  the  Great  I>asin  least  so;  a  large  proportion  of  the 
alkali  salts  being  evidently,  in  the  latter  case,  contained  in  the 
form  of  organic  salts,  which  in  the  ash  become  carbonates. 

It  will  be  noted  that  the  saltbush  hay  contains  nearly  one- 
fifth  of  its  (airdry)  weight  of  ash.  of  which  nearly  4Orr  is 
common  salt.  It  therefore  has  a  distinctly  salty  taste,  and  is 
34 


530 


SOILS. 


* 

^ 

2 

oomg             85a2 
oq  t^oo  *o               q  oo  cS  o 

o  m 
1" 

o 

•ORAGE  CR< 

•to  (  ^E 

6- 

pfy  !«}f 

o 

IOO.OO 

O 

•S03DS3UB3 

? 

S-JSJi^  J=3S 

T  •*• 

8 

xsjdujy 

«         «    -                    i- 

8 

8 

j'^ESJ    AjlpUd 

00 

r?||  ?«w« 

O    0 

8  ' 

oo'ool 

•SSplOJIB 

s 

r>«-iO>-|p|      ro     t-N.N»o»-. 

*o 

o 
o 

LANTS. 

snjoqojods 

^ 

m  i^oo  ^-         e*    *£>  «  ^r  PI 

8 

8 

BH 

•B}BDlds 

- 

owy^     «     K^o  o 

o 

o 

3 

SI(q3IlSIQ 
_'SSEj3)lEQ 

M 

** 

8 

8 

SALINE  AN 

'sn^EjnDtuijaA 

00 

o 
c 

i» 

o 
o 

O 

CO 

U 

CO 

'aaiqdiuEg  Aqsng 

q" 

IP?  1«S5 

O    (^ 

0 

O 

^BDOEqtUIOS 

^ 

*2K?a  a  MJS 

m.« 

8 

uBiiBjjsnv" 

M 

—  "Y— 

if" 

8 

b 

b 

Ash,  airdried  plant 

Potash  (KaO)  
Soda  (Na2O)  
Lime  (CaO)  
Magnesia  (  MgO)  
Br.  ox.  of  Manganese  Mn3O4 
Peroxid  of  Iron  (Fe2Os)  
Alumina  (A12O3)  
Silica  
Phosphoric  acid  (PaO6)  
Sulf  uric  acid  (SO3)  
Chlorin,  per  cent  

0 
O 

"rt 
O 

I 

SALINE  AND  ALKALI  LANDS. 


551 


always  moist  to  the  touch,  containing-  ordinarily  over  i$r/( 
of  moisture.  It  is  therefore  much  liked  by  stock  when  fed 
intermixed  with  other  hay,  and  thus  supplies  all  the  salt 
needed  by  cattle.  The  greasewood  is  much  less  liked  by  stock, 
and  bushy  samphire  is  wholly  rejected  by  them.  Comparing 
with  these  fleshy  plants  the  ash  of  the  two  grasses,  the  first  a 
world-wide  "  salt  grass."  the  other  a  common  grass  of  the 
American  arid  region,  we  note  that  not  only  do  they  contain 
much  less  soluble  ash  than  the  saltbnshes,  but  especially  much 
smaller  amounts  of  sodium  salts;  proving  that  even  when 
growing  in  company  with  the  saltbushes  on  strongly  impreg- 
nated land,  they  can  repel  from  absorption  these  to  them  use- 
less or  injurious  salts.  But  in  the  case  of  the  "  shad  scale." 
also  a  "  saltbush  "  of  the  Great  Basin,  the  ash-content  is 
remarkably  low — only  about  one-fifth  of  that  of  its  Australian 
relative — and  it  differs  widely  from  the  latter  in  having  but 
a  very  low  proportion  of  soda,  and  a  verv  high  one  of  lime 
and  potash,  approaching  in  these  respects  to  our  usual  forage 
crops:  and  being  also  fairly  rich  in  nitrogen,  it  forms  accept- 
able browsing  when  other  pasture  plants  are  scarce.  Tt  there- 
fore does  not  exert  the  laxative  action  produced  by  the  exclu- 
sive feeding  on  the  more  saline  herbages. 

'The  exceptionally  high  ash-content  of  the  cactus  or  prickly 
pear,  also  given  in  the  table,  arises,  it  will  be  noted,  not  from 
the  soluble  salts  but  from  the  absorption  of  extraordinarily 
high  proportions  ot  lime  and  magnesia.  Owing  probably  to 
the  latter  substance,  and  also  the  oxalate  form  in  which  lime 
is  usually  found  in  the  cactus  tribe,  this  plant  when  used  as 
forage  is  also  somewhat  laxative. 

Altogether,  this  table  offers  remarkable  examples  of  wide 
differences  in  the  kind  and  amount  of  ash  ingredients  ab- 
sorbed by  plants  growing  upon  similar  soils  and  under  identi- 
cal climatic  conditions;  indicating  a  selective  power  which  no 
merely  physical  theory  of  soil-action  in  plant  growth  can  ex- 
plain. 

Injury  to  Plants  /"/'<>///  ///(-  I'arioiis  Sails. — The  early  ob- 
servers, especially  Contejean,  \\ere  predisposed  from  their 
observations  of  lime  on  vegetation  to  ascribe  the  action  of  salt 
upon  marine  vegetation  to  the  sodium  component.  But  the 
wi:!e  differences  in  the  effects  of  different  sodium  compounds. 


532  SOILS. 

notably  of  common  salt  and  Glaubers  salt,  led  some  to  the  con- 
clusion that  the  acidic  ingredients  are  the  chief  determin- 
ing factors.  Moreover,  it  was  soon  found  that  a  single  salt 
is  more  injurious  than  a  mixture  of  several,  such  as  sea 
water.  This  also  led  to  the  inference  that  the  varying  degree 
of  dissociation  of  these  salts  essentially  influences  the  effects. 

Kearney  and  Cameron  have  investigated  these  relations,1  and  hav< 
by  artificial  cultures  in  solutions  of  varying  concentration  and  com- 
position  studied  the  behavior  of  plant  roots  and  the  limits  of  theii 
endurance.  They  found  for  the  several  salts  occurring  in  alkali  soils, 
taken  separately,  the  following  figures,  in  100,000  parts  of  water: 

Magnesium  sulfate 7 

"  chlorid 12 

Sodium  carbonate  26 

"  sulfate 53 

"  chlorid 116 

"  bicarbonate 167 

Calcium    chlorid ij377 

It  will  be  noted  that  in  many  respects  the  results  given  in  this  table 
stand  in  marked  contrast  to  the  facts  observed  in  alkali  lands  every- 
where ;  and  therefore  while  interesting  physiologically,  are  not  directly 
applicable  to  practice.  Magnesium  sulfate,  which  according  to  this 
table  is  the  most  injurious  of  all,  is  a  common  ingredient  of  alkali  lands 
from  Wyoming  to  New  Mexico,  as  also  is  sodium  sulfate ;  yet  there, 
as  well  as  in  the  Musselshell  valley  in  Montana,  and  at  many  other 
points,  it  shows  no  specially  deleterious  action  either  upon  native  or 
cultivated  plants,  and  in  Europe  as  well  as  in  New  England  the  mineral 
kieserite  is  freely  used  as  a  fertilizer  at  many  points.  That  sodium 
sulfate  should  be  twice  as  harmful  as  sodium  chlorid  or  common  salt, 
and  half  as  harmful  as  the  carbonate  or  black  alkali,  is  again  wholly 
contrary  to  actual  experience,  which  as  shown  elsewhere  in  this  chapter, 
indicates  that  the  majority  of  plants  will  tolerate  between  three  and 
four  times  as  much  of  sodium  sulfate  as  of  common  salt ;  while  the  ratio 
of  tolerance  as  against  the  carbonate  seems  sometimes  to  rise  as  high 
as  ten  to  one. 

It  is  clearly  evident,  however,  that  it  is  the  metallic  or  basic  ingre- 
dient that  in  the  main  determines  the  toxicity  of  these  salts.  The 
universal  presence  of  lime  in  some  form  in  all  alkali  lands  doubtless 
1  Report  No.  71,  TJ.  S.  Deo't  of  Agriculture,  1902. 


SALINE  AND  ALKAL!  LANDS.  533 

explains  the  discrepancies  mentioned,  since  lime  is  especially  potent  in 
counteracting  the  injurious  effects ;  thus  throwing  additional  light  upon 
the  importance  of  the  lime-content  of  alkali  soils  proper,  and  also  upon 
the  causes  of  the  narrow  limitations  of  the  littoral  (marine  saline)  flora ; 
inasmuch  as,  unlike  alkali  soils,  marine  alluvial  lands  are  by  no  means 
always  calcareous.  Cameron  goes  so  far  as  to  attribute  the  favorable 
effects  of  gypsum  upon  black  alkali  not  so  much  to  the  conversion  of 
the  latter  into  neutral  sulfate,  as  to  the  effect  of  gypsum  solution  in 
counteracting  the  saline  effects.  This  interpretation,  however,  seems 
rather  far-fetched,  since  there  can  be  no  question  about  the  double 
decomposition  of  gypsum  with  carbonate  of  soda ;  or  the  intense  injur- 
iousness  of  carbonate  of  soda  in  the  actual  corrosion  of  vegetable 
tissues.  The  corresponding  protective  influence  of  various  salts,  more 
especially  of  those  of  lime,  against  the  injurious  effects  of  pure  common 
salt  on  marine  animals,  has  already  been  mentioned  (chapter  20,  page 
380),  and  later  investigations  by  Osterhout  on  marine  algae,  show  the 
same  relation  to  hold  true  for  them  also. 

Reclamation  of  Marine  Saline  Lands  for  Culture. — The 
reclamation  of  sea-coast  lands  and  marshes  for  agricultural 
use  is  based  in  general  upon  the  same  methods  as  those  al- 
ready outlined  for  alkali  lands  in  chapter  20;  except  that  in 
this  case  no  chemical  neutralization  is  possible,  since  common 
salt  cannot  be  changed  by  any  practically  feasible  means.  It 
must  be  removed  by  leaching,  and  this,  in  the  humid  countries 
in  which  such  reclamations  have  chicllv  been  made,  is  usually 
done  by  the  agency  of  rains,  aided  by  ditching.  The 
"  polder  "  lands  thus  reclaimed  along  the  shores  of  the  Xorth 
Sea,  from  Belgium  to  Prussia,  are  especially  esteemed  for 
their  productiveness,  doubtless  owing  to  the  alluvium  of  the 
numerous  rivers  tributary  to  that  sea.  which  is  distributed 
along  its  shores  and  in  the  numerous  inlets  and  bays.  The 
tides  are  of  course  excluded  by  dikes  provided  with  gates 
opening  outward,  so  as  to  permit  of  the  outflow  of  rain- 
or  irrigation-water  used  for  leaching  purposes. 

Out  of  reach  of  stream  alluvium  no  exceptional  fertility  is 
to  be  expected  of  sea-shore  lands,  which  then  commonly  assume 
the  form  of  sand  dunes  or  bars,  incapable  of  nourishing  any 
cultural  vegetation.  Of  the  latter,  the  groups  listed  below  as 
tolerant  of  alkali  salts,  may  also  be  considered  with  reference 


534  SOILS. 

to  reclaimed  sea-shore  lands;  the  first  cereal  to  succeed  being 
usually  barley,  the  first  root  crop,  beets.  Asparagus  is  also 
available  while  salt  is  being  leached  out. 


THE  VEGETATION  OF  ALKALI   LANDS. 

The  general  character  of  alkali-land  vegetation  is  not  unlike 
that  of  saline  sea-shore  lands ;  some  species  of  plants  are  com- 
mon to  both,  but  the  alkali  lands  harbor  a  much  greater  variety 
of  plants,  owing  to  the  differences  in  climates  and  soils  as 
v;e!l  as  to  the  nature  of  the  impregnating  salts.  Moreover, 
owing  to  the  very  causes  which  underlie  the  presence  of  these 
salts,  viz,  aridity,  the  xerophile  or  dry-land  character  of  the 
alkali-land  flora  is  much  more  pronounced  than  that  of  the 
saline  sea-shore  vegetation.  In  view  of  the  very  complex 
conditions,  the  discussion  of  the  alkali-flora  is  of  necessity 
much  more  complex  than  that  of  the  marine  group;  and  the 
data  for  its  full  elucidation  with  respect  to  the  nature  of  the 
soils  and  salts  are  as  yet  very  incomplete. 

RECLAIMABLE     AND     IRRECLAIMABLE     ALKALI     LANDS     AS     DIS- 
TINGUISHED  BY  THEIR   NATURAL   VEGETATION. 

While,  as  shown  above  (chapter  20),  the  adaptation  or 
non-adaptation  of  particular  alkali  lands  to  certain  cultures 
may  be  determined  by  sampling  the  soil  and  subjecting  the 
teachings  to  chemical  analysis,  it  is  obviously  desirable  that 
some  other  means,  if  possible  available  to  the  farmer  himself, 
should  be  found  to  determine  the  reclaimability  and  adapta- 
tion of  such  lands  for  general  or  special  cultures. 

In  alkali  lands,  as  in  others,  the  natural  plant-growth  affords 
such  means,  both  as  regards  the  quality  and  quantity  of  the 
saline  ingredients.  The  most  superficial  observation  shows/ 
that  certain  plants  indicate  extremely  strong  alkali  lands 
where  they  occupy  the  ground  alone ;  others  indicate  pre- 
eminently the  presence  of  common  salt ;  the  presence  or  ab- 
sence of  still  others  form  definite  or  probable  indications  of 
reclaimability  or  non-reclaimability.  Many  such  characteris- 
tic plants  are  well  known  to  and  readily  recognized  by  the 
farmers  of  the  alkali  districts.  "  Alkali  weeds  "  are  com- 


SALINE  AND  ALKALI  LANDS.  535 

monly  spoken  of  almost  everywhere;  but  the  meaning  of  this 
term — /.  c.,  the  kind  of  plant  designated  thereby — varies  ma- 
terially from  place  to  place,  according  to  climate  as  well  as  the 
quality  of  the  soil.  It  is  obvious  that  if  these  characteristic 
plants  were  definitely  observed,  described  and  named,  while 
also  ascertaining  the  amount  and  kind  of  alkali  they  indicate 
as  existing  in  the  land,  lists  could  be  formed  for  the  several 
regions,  which  would  indicate,  in  a  manner  intelligible  to  the 
farmer  himself,  the  kind  and  degree  of  impregnation  with 
which  he  would  have  to  deal  in  the  reclamation  work;  thus 
enabling  him  to  go  to  work  on  the  basis  of  his  own  judgment, 
without  previous  chemical  examination. 

A  study  of  the  lands  of  California  having  this  purpose  in 
view,  was  undertaken  in  the  years  iS(>S  and  1899  by  the  Cali- 
fornia Station;  but  lack  of  funds  prevented  its  prosecution 
beyond  the  ascertainment  of  those  plants  the  abundant  oc- 
currence of  which  prove  the  land  to  be  irreclaimable  without 
the  use  of  the  universal  remedy,  \'r/.,  underdrainage,  which  on 
the  large  scale  is  usually  beyond  the  means  of  the  land-seeker. 
The  botanical  field  work  and  collection  of  soil  samples  was 
carried  out  by  Mr.  Jos.  I'urtt  Davy:  the  chemical  work,  as 
heretofore,  being  done  by  Dr.  K.  If.  Loughridge.  The  re- 
sults here  reported  are  therefore  essentially  their  joint  work. 
It  is  hoped  that  in  the  future,  a  more  comprehensive  study  and 
close  comparison  of  the  native  vegetation  with  the  chemical 
determination  of  the  quality  and  kind  of  alkali  corresponding 
to  certain  plants,  or  groups- of  plants,  naturally  occurring  on 
the  land,  may  enable  us  to  conic  to  a  sufficiently"  close  estimate 
of  the  nature  and  capabilities  of  the  latter  from  the  native 
vegetation  a'mic.  or  with  the  aid  of  test  plants  purposely 
grown,  for  the  fanners'  purposes. 

Plants  Indicating  Irreclaimable  Lands. — The  plants  herein- 
after mentioned  and  figured  arc.  then,  to  be  understood  as 
indicating,  7v'//r//<V(T  ///<"y  occupy  the  ground  as  an  abundant 
and  luxuriant  growth,  that  such  land  is  irreclaimable  for  ordi- 
nary crops,  unless  underdrained  for  the  purpose  of  washing 
out  surplus  salts.  The  occurrence  merely  of  scattered,  more  or 
less  stunted  individuals  of  these  plants,  while  a  sure  indi- 
cation of  the  presence  of  alkali  salts,  docs  not  necessarily  show 
that  the  land  is  irreclaimable. 


536  SOILS. 

The  plants  which  may  best  serve  as  such  indicators  in 
California  are  the  following: 

Tussock-grass  (Sporobolus  airoides  Torr.),  Fig.  82. 

Bushy  Samphire  (Allenrolfea  occidentalis  (Wats.)  Ktze. ), 
Fig.  83. 

Dwarf  Samphire  (Salicornia  subterminalis  Parish,  and 
other  species),  Fig.  84. 

Saltwort  (Suaeda  torreyana  Wats.,  and  5".  suffrntescens, 
Wats.),  Fig.  85. 

Greasewood  (Sarcobatus  vernuculatus  (Hook.)  Torr.), 
Fig.  86. 

Alkali-heath  (Frankenia  grandi folia  campestris  Gray), 
Fig.  87. 

Cressa  (Cressa  truxillensis  Choisy),  Fig.  88,  perhaps 
identical  with  C.  cretica  auct. 

Salt-grass  (Distichlis  spicata},  Fig.  89. 

TUSSOCK  GRASS  (Sporobolus  airoides,  Torr.)  ;  Fig.  82. 
("  Buneh  grass"  of  New  Mexico). 

The  three  sets  of  Tussock-grass  soil  which  have  been 
analyzed  show  that  the  total  amount  of  all  salts  present  is 
in  no  case  less  than  49,000  pounds  per  acre,  to  a  depth  of 
four  feet;  and  that  it  sometimes  reaches  the  extraordinarily 
high  figure  of  499,000  pounds.  Of  these  amounts  the  neutral 
salts  (Glauber's  salt  and  common  salt)  are  usually  in  the 
heaviest  proportion  (Glauber's  salt,  19,600  to  323,000  pounds 
per  acre;  common  salt,  3,500  to  172,800)  ;  the  corrosive  sal- 
soda  varying  from  3,000  to  44,000  pounds. — Tussock-grass 
apparently  cannot  persist  in  ground  which  is  periodically 
flooded.  It  is  of  special  importance  because  it  is  an  acceptable 
forage  for  stock. 

Tussock-grass  is  a  prevalent  alkali-indicator  in  the  hot, 
arid  portions  of  the  interior,  from  the  upper  San  Joaquin 
Valley,  the  Mojave  desert,  and  southward;  also  through 
southern  Nevada  and  Utah  as  far  east  as  Kansas  and  Ne- 
braska. In  the  San  Joaquin  Valley  it  has  not  been  found  far- 
ther north  than  the  Tulare  plains,  although  east  of  Reno  it 
occurs  near  Reno.  Coville  observes  that  in  the  Death  Valley 
region  "  it  is  confined  principally  to  altitudes  below  i,oob 
meters"  (3.280  feet).  Hillman,  however,  reports  it  from 


SALhNE  AND  ALKALI  LANDS. 


537 


FIG.  8a  — Tussock  Grass — S^ori'Mut  airoiJcs  Torr. 


538  SOILS. 

near  Reno,  Nevada,  at  an  altitude  which  cannot  be  much  less 
than  4.500  feet. 

The  tussocks  formed  by  this  grass,  which  are  unfortunately 
not  shown  in  the  figure,  sometimes  appear  as  veritable  little 
grass  trees,  and  when  denuded  by  the  browsing  of  cattle  seem 
like  trunks  18  and  20  inches  high.  It  is  therefore  very  easily 
recognized;  but  it  should  be  noted  that  in  view  of  the  extra- 
ordinary range  of  its  tolerance,  shown  above,  its  scattered 
occurrence  does  not  necesarily  indicate  irreclaimable  land. 

BUSHY  SAMPHIRE.  (Allenrolfca  occidentalis  (Wats.) 
Ktze.)  Fig.  83. 

This  plant  is  locally  called  greasewood,  but  as  this  name  is 
much  more  commonly  used  for  Sarcobatus  venniculatus,  it 
seems  best  to  call  Allenrolfea  "  bushy  samphire,"  as  it  closely 
resembles  the  true  samphire  (Salicornia). 

Bushy  Samphire  usually  grows  in  low  sinks,  in  clay  soil 
which  in  winter  is  excessively  wet,  and  in  summer  becomes  a 
"  dry  bog."  Wherever  the  plant  grows  luxuriantly  the  salt 
content  is  invariably  high,  the  total  salts  varying  from  327,- 
ooo  pounds  per  acre,  to  a  depth  of  three  feet,  to  494,520 
pounds  in  four  feet.  The  salts  consist  mainly  of  Glauber's  and 
common  salts  (a. maximum  of  about  275,000  pounds  each); 
salsoda  varies  from  2,360  to  4,800  pounds  per  acre.  The 
percentage  of  common  salt  and  total  salts  is  higher  than  for 
any  other  plant  investigated,  and  the  content  of  Glauber's  salt 
is  also  excessive.  The  areas  over  which  this  plant  grows 
must  therefore  be  considered  among  the  most  hopeless  of 
alkali  lands,  for  although  its  salts  are  "  white,''  submergence 
during  winter  precludes  the  growth  of  Australian  saltbushes. 
Full  underdrainage  alone  could  reclaim  the  soil-areas  it  occu- 
pies. Bushy  Samphire  is  common  on  low-lying  alkali  lands 
in  the  upper  San  Joaqnin  Valley,  California,  and  extends 
northward  along  the  eastern  slopes  of  the  Coast  Range  to 
Suisun  Bay.  It  is  also  abundant  in  the  Death  Valley  region, 
apparently  overlapping  the  southward  range  of  the  Sarco- 
batus, the  greasewood  properly  so-called. 

DWARF  SAMPHIRE  (Salicornia  subtcnninalis,  Parish,  and 
other  species  of  the  interior)  ;  Fig.  84. 

The  three  or  four  species  of  Dwarf  Samphire  which  grow 


SALINE  AND  ALKALI  LANDS. 


539 


FIG.  $3.— Hushy  £a,mpkire—slffenr0l/e<i  occiiienliiiis  ^ia.  Wats.)  G.  Ktze. 


540 


SOILS. 


in  the  interior  valleys  of  the  State  are  not  usually  very  abund- 
ant, save  locally.  Wherever  the  species  do  occur,  however, 
they  may  be  considered  as  indicating  excessively  saline  soils. 


FIG.  84. — Salicornia  subterminalis.  Alkali  samphire. 

A.  Much-branched  form. 

B.  Slender  form. 

C.  Flower  with  the  perianth  removed  showing  the  simple  pistil  and  the  two  stamens. 

D.  Portion  of  flowering  spike,  showing  two  joints.     The  flowers  are   impressed   in  the  joints   in 
opposite  clusters  of  three.     In  each  cluster  the   middle   flower  stands  slightly  above  the  two  laterals 
as  shown  in  the  lower  joint. 

Dwarf  Samphire  soil  has  shown  a  total  salt  content  of  441,- 
880  pounds  per  acre  in  a  depth  of  four  feet.  The  neutral 
Glauber's  salt  amounts  to  314.000  pounds,  almost  as  much  as 
in  Tussock-grass  soil;  common  salt  up  to  125,640  pounds 


SALINE  AND  ALKALI  LANDS.  541 

while  the  salsoda  varies  from  2,200  to  12,000.  We  may  con- 
sider the  plant  as  indicative  of  almost  the  highest  percentage  of 
common  salt,  Glauber's  salt  and  total  salts.  Like  the  preceding 
species  it  indicates  land  strongly  charged  with  salts,  more 
especially  common  salt,  and  susceptible  to  cultivation  only 

after  reclamation  by  under-drainage. 

• 

Salicornia  subterminalis,  S.  hcrbacca  (L. ),  S.  mucronata, 
and  another  species,  all  occurring  inland,  differ  materially  in 
habit  and  botanical  characters  from  the  one  so  conspicuous  in 
submerged  salt  marshes  along  the  seashore;  but  all  alike  indi- 
cate strongly  saline  soils,  reclaimable  only  by  thorough  drain- 
age. 

SALT-WORT  (Snacda  torrcyana,  Wats.,  S.  snffntfcscens, 
Wats.,  and  perhaps  one  other  species)  ;  Fig.  85. 

Samples  of  saltwort  soil  from  Bakersfield  and  Byron 
Springs,  California,  taken  to  a  depth  of  one  foot  and  three 
feet  respectively,  show  that  this  plant  grows  luxuriantly  in  a 
soil  containing  130,000  pounds  of  total  salts  per  acre  in  the 
first  foot,  and  with  10,480  pounds  of  the  noxious  salsoda,  and 
39,760  pounds  of  common  salt  in  three  feet;  while  only  a 
sparse  growth  is  found  on  soils  containing  only  3.700  pounds 
of  salts  in  three  feet.  It  thus  appears  to  indicate  a  lower 
percentage  of  salsoda  than  does  Greasewood.  but  a  higher 
percentage  than  Bushy  Samphire.  Further  investigation  is 
necessary  to  determine  the  exact  relation  of  the  different  salts 
to  the  growth  of  the  plant,  and  as  to  whether  carbonates  occur 
in  large  quantity;  but  enough  data  have  been  gathered  to  show 
that  a  luxuriant  growth  of  Suaeda  torreyana  indicates  a  soil 
reclaimable  only  by  thorough-drainage. 

Suaeda  torreyana  occurs  on  low  alkali  lands  throughout 
the  State  of  California,  from  San  Bernardino  to  Honey  Lake, 
in  the  desert  sinks,  and  in  the  Great  Valley,  in  appropriate 
locations.  Sometimes  it  is  replaced  by  X.  snffnitcsccits  and 
perhaps  other  species,  but  all  the  saltworts  appear  to  grow  in 
similar  habitats,  and  it  is  probable  that  the  soil-conditions  are 
practically  the  same  for  all  these  species.  They  indicate  land 
too  heavily  impregnated  for  the  growth  of  ordinary  crops, 
but  which  will  perhaps  allow  the  Australian  saltbush  to  suc- 
ceed. 


542 


SOILS. 


FIG.  85. — Saltwort — Suaeda  Torreyana,  Wats. 

GREASEWOOD  (Sarcobatus  vcrmiciilatus  (Hook.  Torr.)  ; 
Fig.  86. 

This,  the  true  Grcascwood  of  the  desert  region  east  of  the 
Sierra  Nevada,  and  not  either  of  the  plants  known  under  that 
name  in  the  San  Joaquin  Valley  and  in  Southern  California, 
invariably  indicates  a  heavy  impregnation  of  the  land  with 
hlack  alkali  or  carbonate  of  soda.  Since,  as  before  stated, 
black  alkali  is  most  likely  to  occur  in  low  ground,  we  fre- 
quently find  the  true  greasewood  forming  bright  green 
patches  in  the  swales,  and  on  the  benches  of  periodic  streams, 
as  well  as  on  the  borders  of  alkali  ponds  or  lakes.  Stock  un- 
accustomed to  it  will  frequently  go  to  these  patches  on  a  run,. 


SALINE  AND  ALKALI  LANDS. 


543 


only  to  turn  away  badly  disappointed  after  taking  a  few  bites, 
the  plant  being  both  bitter  and  salty. 


Ki<;.  S'i.  —  I  .rcasewood  (proper'  —  . 


vtrmicuhtus  (Ilooki  Torr. 


A.    Ap 

I  .    Spii 


lira 


I'.r.i 


iMr.inre  of  a  hruuh  when  not  in  hl<>«som. 
y-brjiirlilet  from  the  s.inie. 
irhlct  luMring  <  ones  of  in. ile  flowers, 
e  of  m.ile  Mowers,  enlarged. 


O.    Vertical  section  through  a  fruit,  showing  tlie  seed  with  its  curved  embryo,  '  enlarged!. 

Where  a  luxuriant  growth  of  this  plant  i<  found,  the  soil 
may  contain  from  38.000  to  i  i-.ooo  pounds  of  total  salts  per 
acre,  of  which  sometimes  nearly  half  is  carbonate  of  soda; 
the  content  of  common  salt  is  usually  l<i\v.  and  (ilanber's  salt 


544 


SOILS. 


or  sulfate  of  soda,  sometimes  with  considerable  proportion  of 
epsom  salt,  forms  a  variable  proportion  of  the  total. 

Greasew'ood  is  distinctly  a  plant  of  the  Great  Basin,  only 
reaching  California  in  the  adjacent  counties  of  Lassen,  Alpine, 
Mono,  and  northern  Inyo.  It  is  very  abundant  on  the  lower 
levels  of  Honey  Lake  valley,  Cal. 

The  Sarcobatus  is  chiefly  found  on  silty  or  sandy  soils  of 
good  native  fertility  (see  page  445,  chapter  22),  so  that  when 
its  excess  of  salsoda  is  neutralized  by  means  of  gypsum,  the 
land  becomes  very  productive.  Unfortunately  the  cost  of  the 
amount  of  gypsum  required  to  render  such  soils  adapted  to  the 
tolerance  of  most  culture  plants  is  often  prohibitive;  but 
where  the  correction  of  only  small  spots  is  called  for,  the 
"  white  alkali  "  resulting  from  the  gypsum  treatment  would 
be  tolerated  by  many  culture  plants. 

ALKALI-HEATH  (Frankcnia  grandifolia  campestris  Gray)  ; 
Fig.  87. 


FlG.  87. — Alkali-Heath — Frankenia  grandifolia  campestris  A  Gray. 


Alkali-heath  is  perhaps  the  most  widely  distributed  of  any 
of  the  California  alkali   plants.     Its  perennial,   deep-rooting 


SALINE  AND  ALKALI  LANDS.  545 

habit  of  growth,  and  flexible,  somewhat  wiry  rootstock, 
which  enables  it  to  persist  even  in  cultivated  ground,  render  it 
a  valuable  plant  as  an  alkali  indicator.  The  salt-content 
where  Alkali-heath  grows  luxuriantly  is  invariably  high, 
ranging  from  64,000  to  282,000  pounds  per  acre;  salsoda 
varies  from  680  to  19,590  pounds;  common  salt  ranges  from 
5,000  to  10,000  pounds.  Such  soils  would  not  be  benefited  by 
the  application  of  gypsum,  as  the  salts  are  already  largely  in 
the  neutral  state.  Of  useful  plants  only  Saltbushes  and  Tus- 
sock-grass are  likely  to  flourish  in  such  lands,,  when  not  too 
wet. 

While  Alkali-heath  is  thus  one  of  the  most  alkali-tolerant 
plants,  it  is  at  the  same  time  capable  of  growth  with  a  mini- 
mum of  salts  (total  salts  3,700  pounds,  salsoda  680  pounds). 
Where  only  a  sparse  growth  of  this  plant  occurs,  therefore,  the 
land  should  not  be  condemned  until  a  chemical  examination 
of  the  soil  has  been  made. 

Alkali-heath  is  found  on  soils  of  very  varying  physical  tex- 
ture and  degrees  of  moisture;  while  on  soils  of  uniform 
texture  and  moisture-conditions,  but  differing  in  chemical 
composition,  it  varies  with  the  varying  salt-content. 

It  has  been  found  that  Australian  saltbush  (Atriplcx  seini- 
baccata)  can  be  successfully  grown  on  the  "goose-lands,"  of 
the  Sacramento  Valley,  on  soil  producing  a  medium  crop  of 
Alkali-heath ;  it  remains  to  be  shown  whether  it  will  do 
equally  well  on  soils  producing  a  dense  and  luxuriant  growth 
of  the  same. 

Alkali-heath  is  widely  distributed  throughout  the  interior 
valleys  of  California;  a  closely  related  form  grows  in  the  salt- 
marshes  of  the  sea-coast. 

CRKSSA  (  Cressa  crcticti  tnt.villcnsis  Choisy)  ;  Fig.  SS. 

Cressa  soils  show  a  low  percentage  of  the  noxious  salsoda, 
but  comparatively  heavy  total  salts  (161.000  to  jSj.ooo 
pounds  per  acre.)  Common  salt  varies  from  5,760  to  20,840 
pounds  per  acre  in  four  feet.  The  maximum  is  lower  than  in 
the  case  of  Alkali-heath,  but  Cressa  seems  to  bo  much  more 
closely  restricted  to  strong  alkali  than  docs  the  former  species. 
Cressa  appears  to  be  as  widely  distributed  through  the  in- 
terior valleys  of  California  as  Alkali-heath.  The  Cressa  is  a 
35 


546  SOILS. 

cosmopolitan  plant,  occurring,  as  its  name  indicates,  on  the 
Ionian  Islands,  as  well  as  in  North  Africa,  Syria,  and  other 
arid  countries  of  the  world. 

SALT-GRASS,  Distichlis  spicata. — This  grass  is  of  world 
wide  distribution,  and  always  indicates  a  sensible  content  of 
soluble  salts,  without  apparently  any  special  preference  for 
either  of  the  three  most  commonly  occurring  ones.  Its  maxi- 
mum tolerance,  as  will  be  seen  by  the  preceding  table,  is  very 
high,  yet  at  the  same  time  it  wrill  grow  luxuriantly  on  lands 
containing  so  little  that  other  saline  plants  like  the  samphires, 
saltwort  or  greasewood  will  refuse  to  grow.  On  the  shores  of 


<  FIG.  88, — Cressa — Cressa  cretica  truxillensis,  Choisy. 

Honey  Lake,  California,  it  may  often  be  seen  incrusted  with 
the  salts  of  the  water  concentrated  by  a  long  season  of 
drought,  yet  maintaining  life,  though  somewhat  stunted.  On 
lands  lightly  impregnated,  stock  will  often  eat  it  quite  freely, 
so  that  it  has  been  mistaken  for  Bermuda  grass,  to  which  its 
habit  and  foliage  bears  some  resemblance.  But  Bermuda 
grass,  while  not  as  sensitive  to  alkali  as  most  forage  grasses, 
will  probably  not  bear  much  over  12,000  pounds  per  acre. 

The  mere  presence  of  the  salt  grass  cannot  therefore  be 
taken  as  a  definite  indication  of  anything  more  than  that  there 
is  an  unusual  amount  of  salts  in  the  soil ;  whether  or  not  there 


SALINE  AND  ALKALI  LANDS. 


547 


548  SOILS. 

is  more  than  will  be  tolerated  by  the  ordinary  culture-plants, 
must  be  judged  either  from  the  accompanying  plants,  or  by 
experiment  or  analysis. 

Relative  Tolerance  of  the  Different  Species. — The  follow- 
kig  table  shows  in  systematic  order  the  tolerance  of  the  several 
plants  discussed  above,  for  the  different  salts,  so  far  as  the 
data  available  permit.  The  column  marked  optimum  shows 
under  what  proportions  of  salts  the  plants  grew  in  about  equal 
luxuriance,  therefore  under,  apparently,  the  most  favorable 
conditions.  Both  above  and  below  the  proportions  mentioned 
in  that  column,  the  luxuriance  (size)  and  (usually)  the 
abundance  of  the  plants  was  less;  showing  that  while  excess- 
ive amounts  of  salts  depressed  their  welfare,  yet  they  also 
suffered  when  the  proportions  dropped  below  a  certain  point. 
Whether  this  was  partly  or  wholly  the  result  of  competition 
with  other  plants,  is  an  unsettled  question. 


SALINE  AND  ALKALI  LANDS. 


549 


TABLE  SHOWING  MAXIMUM,  OPTIMUM,  AND  MINIMUM  OF  SALTS  TOLERATED  BY  EACH 
OF  THE  SEVERAL  ALKALI  PLANTS. 


Pounds  Per  Acre  in  feet 

Optimum. 

Maximum. 

Minimum. 

Total  Salts. 

494.320 
441,880 
(      381,960  1 
'I        'M,3oo  f 
281,960 
130,000 
58,560 

494,520 
441,880 

499,040 

281,960 
153,020 
5S,56o 
499,040 

44,46o 
19,590 
18,720 

12,120 
12,120 
5,440 
4,800 

275,l6o 
125,640 
52,900 
20,840 

212,080 

172,800 
3,680 

314,040 
277,640 
275,5J'> 
JJ.?,  2.x> 

104,040 
36,160 
323,200 

135,060 
441,880 

3-720 
161,160 
3,720 
2,400 
49,000 

3,040 
680 
1,280 

2,200 
1,1  2O 

680 
1,500 

56,800 
125,040 
1,040 
5.760 
I,O4O 

3,530 
|60 

314,040 
50,080 

134,880 

1,560 

i,5<x> 
060 
19,640 

Alkali-heath  

Saltworts  

Greasewood  

49,000 

23,000 
(      *  19,  590) 
i               680) 
18,720 

12,120 
10,480 
5.440 
4,800 

2I2,o8o 
125,640 
39,7<» 
20,840 
1             lO.lSol 

1            S,7'*>  \ 
6,200 
3,680 

3  '4,  040 
277,040 
275.520 
(       275,520) 

1         34,53"! 
44.i»o 

3'>,l6o 

19,640 

Carbonate  (Salsoda). 

Alkali-heath  

Chloride  (Common  Salt). 

Sulf  hates  (Glauber's  salt). 

H      1      Si        I  i    > 

*  This  plant  grows  with  equal  luxuriance  in  soils  containing  only  680  pounds  of  carbonate*. 


APPENDICES 


APPENDIX  A. 

DIRECTIONS  FOR  TAKING  SOIL  SAMPLES.    ISSUED  BY  THE 
CALIFORNIA  EXPERIMENT  STATION. 

IN  taking  soil  specimens  for  examination  by  the  Agricultural  Ex- 
periment Station,  the  following  directions  should  be  carefully  observed  : 
always  bearing  in  mind  that  the  examination,  and  especially  the 
analysis,  of  a  soil  is  a  long  and  tedious  operation,  which  cannot  be 
indefinitely  repeated. 

First. — Do  not  take  samples  at  random  from  any  points  on  the  land, 
but  consider  what  are  the  two  or  three  chief  varieties  of  soil  which, 
with  their  intermixtures,  make  up  the  cultivable  area,  and  carefully 
sample  these,  each  separately;  then,  if  necessary,  sample  your  particular 
soil,  noting  its  relation  to  these  typical  ones. 

Second. — As  a  rule,  and  whenever  possible,  take  specimens  from 
spots  that  have  not  been  cultivated,  nor  are  otherwise  likely  to  have 
been  changed  from  their  original  condition  of  "virgin  soils" — f.g.,  not 
from  ground  frequently  trodden  over,  such  as  roadsides,  cattle-paths,  or 
small  pastures,  squirrel  holes,  stumps,  or  even  the  foot  of  trees,  or  spots 
that  have  been  washed  by  rains  or  streams,  so  as  to  have  experienced  a 
notable  change,  and  not  be  a  fair  representative  of  their  kind. 

Third. — Observe  and  record  carefully  the  normal  vegetation,  trees, 
herbs,  grass,  etc.,  of  the  average  virgin  land ;  avoid  spots  showing 
unusual  growth,  whether  in  kind  or  in  quality,  as  such  are  likely  to 
have  received  some  animal  manure,  or  other  outside  addition. 

Fourth. — Always  take  specimens  from  more  than  one  spot  judged  to 
be  a  fair  representative  of  the  soil  intended  to  be  examined,  as  an 
additional  guarantee  of  a  fair  average,  and  mix  thoroughly  the  earth 
taken  from  the  sain f  deaths. 

Fifth. — After  selecting  a  proper  spot,  pull  up  the  plants  growing  on 
it,  and  sweep  off  the  surface  with  a  broom  or  brush  to  remove  half- 
decayed  vegetable  matter  not  forming  part  of  the  soil  as  yet.  Dig  or 
bore  a  vertical  hole,  like  a  pesthole,  and  note  at  what  depth  a  change 
of  tint  occurs.  In  the  humid  region,  or  in  humid  lowlands  of  the  arid, 

553 


554  APPENDIX  A. 

this  will  usually  happen  at  from  six  to  nine  inches  from  the  surface, 
and  a  sample  taken  to  that  depth  will  constitute  the  "soil." 

In  California  and  the  arid  region  generally,  very  commonly  no  change 
of  tint  occurs  within  the  first  foot,  sometimes  not  for  several  feet ; 
hence,  especially  in  sandy  lands,  the  "  soil  "  sample  will  usually  be  taken 
to  that  depth,  so  as  to  represent  the  average  of  the  first  foot  from  the 
surface  down. 

Samples  taken  merely  from  the  surface,  or  from  the  bottom  of  a  hole, 
have  no  definite  meaning,  and  will  not  be  examined  or  reported  upon. 

Place  the  "  soil "  sample  upon  a  cloth  (jute  bagging  should  not  be 
used  for  the  purpose,  as  its  fibres,  dust,  etc.,  become  intermixed  with 
the  soil)  or  paper,  break  it  up,  mix  thoroughly,  and  put  at  least  a  quart 
of  it  in  a  sack  or  package  properly  labeled,  for  examination. 

This  specimen  will,  ordinarily,  constitute  the  "  soil."  Should  the 
change  of  color  occur  at  a  less  depth  than  six  inches,  the  fact  should  be 
noted,  but  the  specimen  taken  to  that  depth  nevertheless,  since  it  is 
the  least  to  which  rational  culture  can  be  supposed  to  reach. 

In  the  same  way  take  a  sample  of  each  foot  separately  to  a  depth 
of  at  least  three  feet ;  preferably  four  or  five,  especially  in  the  case  of 
alkali  soils,  or  suspected  hardpan. 

Sixth. — Whatever  lies  beneath  the  line  of  change,  or  below  the  min- 
imum depth  of  six  inches,  will  constitute  the  "  subsoil."  But  should 
the  change  of  color  occur  at  a  greater  depth  than  twelve  inches,  the 
"  soil "  specimen  should  nevertheless  be  taken  to  the  depth  of  twelve 
inches  only,  which  is  the  limit  of  ordinary  tillage ;  then  another  speci- 
men from  that  depth  down  to  the  line  of  change,  and  then  the  "  sub- 
soil "  specimens  beneath  that  line. 

The  depth  down  to  which  the  last  should  be  taken  will  depend  on 
circumstances.  It  is  always  necessary  to  know  what  constitutes  the 
foundation  of  a  soil,  down  to  the  depth  of  three  feet  at  least,  since  the 
question  of  drainage,  resistance  to  drought,  root-penetration,  etc.,  will 
depend  essentially  upon  the  nature  of  the  substratum.  In  the  arid 
region,  where  roots  frequently  penetrate  to  depths  of  ten  or  twelve  feet 
or  even  more,  it  is  frequently  necessary  to  at  least  probe  the  land  to 
that  depth  or  deeper.  The  specimens  should  be  taken  in  other  respects 
precisely  like  that  of  the  surface  soil,  each  to  represent  the  average  of 
not  more  than  twelve  inches  Those  of  the  materials  lying  below  the 
third  foot  from  the  surface  may  sometimes  be  taken  at  some  ditch  or 
other  easily  accessible  point,  and  if  possible  should  not  be  broken  up 
like  the  other  specimens. 


APPENDIX  A.  555 

If  there  is  hardpan  or  heavy  clay  present,  an  unbroken  lump  of  it 
should  be  sent,  for  much  depends  on  its  character. 

Seventh. — When  in  the  case  of  cultivated  lands,  it  is  desired  to 
ascertain  the  cause  of  differences  in  the  behavior  or  success  of  a  crop 
on  different  portions  of  the  same  field  or  soil  area,  do  not  send  only 
the  soil  which  bears  unsatisfactory  growth,  but  also  the  one  bearing 
normal,  good  growth,  for  comparison.  In  all  such  cases,  try  to  ascertain 
by  your  own  observations  whether  or  not  the  fault  is  simply  in  the  sub- 
soil or  substrata ;  in  which  case  a  sample  of  surface  soil  sent  for  exam- 
ination would  be  of  little  use.  In  such  examinations  the  soil  probe  will 
be  of  great  service,  and  save  much  digging  or  boring. 

Eighth. — Specimens  of  alkali  or  salty  soils  should  preferably  be  taken 
towards  the  end  of  the  dry  season,  when  the  surface  layers  will  contain 
the  largest  amount  of  salts.  A  special  sample  of  the  first  six  inches 
should  in  that  case  be  taken  separately  by  means  of  a  post-hole  auger, 
and  then,  in  a  different  spot  close  by,  a  hole  four  feet  deep  should  be 
bored,  and  the  earth  from  the  entire  four-foot  column  intimately  mixed 
before  the  usual  quart  sample  is  taken.  Samples  of  the  plants  growing 
on  the  land  should  in  all  cases  be  included  in  the  package,  as  they  in- 
dicate very  closely  the  agricultural  character  of  the  land. 

All  samples  taken  while  the  land  is  wet  should  be  air-dried  before 
sending;  in  the  case  of  alkali  soils  this  is  absolutely  essential. 

Ninth. — All  peculiarities  of  the  soil  and  subsoil,  their  behavior  under 
tillage  and  cultivation  in  various  crops,  in  wet  and  dry  seasons,  their 
location,  position,  "  lay,"  every  circumstance,  in  fact,  that  can  throw 
any  light  on  their  agricultural  qualities  or  peculiarities,  should  be  care- 
fully noted,  and  the  notes  sent  by  mail.  ll'ithout  such  notes,  specimens 
cannot  ordinarily  be  considered  as  justifying  tlie  amount  of  labor  involved 
in  their  examination.  Any  fault  found  with  the  behavior  of  the  land 
in  cultivation  or  crop-bearing  should  be  specially  mentioned  and  de- 
scribed. The  conditions  governing  crop-production  are  so  complex 
that  even  with  the  fullest  information  and  the  most  careful  work,  cases 
are  found  in  which  as  yet  the  best  experts  will  be  at  fault. 


APPENDIX  B. 

SUMMARY  DIRECTIONS  FOR  SOIL— EXAMINATION  IN  THE 
FIELD  OR  ON  THE  FARM. 

WHILE  the  general  principles  upon  which  the  cultural  value  and  adap- 
tations of  lands  should  be  judged,  have  been  given  in  the  text  of  this 
volume,  it  seems  advisable  to  summarize  their  practical  application  to 
land  examination  here,  for  convenient  reference. 

The  directions  given  in  Appendix  I  for  the  sampling  of  soils  having 
been  carried  out,  the  samples  so  taken  may  be  subjected  to  farther 
examination  by  any  intelligent  farmer  to  good  purpose,  and  often  with 
great  saving  of  time  and  expense. 

Spread  the  samples  from  the  several  depths  in  regular  order  upon  a 
table  or  bench,  and  note  the  differences  in  color  and  texture  apparent  to 
the  eye  or  touch,  and  whether  they  will  or  will  not  crush  readily  between 
the  fingers,  wet  and  dry.  Whatever  the  fingers  can  do,  can  similarly  be 
done  by  the  harrow,  cultivator,  clod  crusher  or  roller. 

The  tilling  qualities  of  the  surface  soil  and  immediate  subsoil  are  the 
first  and  most  important  matter  to  be  ascertained ;  including  especially 
their  behavior  to  water.  Place  some  airdried  lumps  in  a  shallow  dish 
with  a  little  water ;  observe  whether  they  take  up  the  water  quickly  or 
slowly,  and  whether  in  so  doing  the  lumps  fall  to  pieces  or  retain  their 
form.  Slow  penetration,  and  maintenance  of  form,  will  at  once  indicate 
a  soil  somewhat  refractory  and  difficult  to  till ;  while  if  the  water  is  taken 
up  easily  and  the  lump  falls  to  pieces,  the  land  is  easily  cultivated  and 
will  absorb  the  rainfall  and  irrigation  water  readily.  The  darkening  of 
the  tint  on  wetting  will  also  give  an  approximate  idea  of  its  humus- 
content. 

Then  take  a  wetted  lump  and  work  it  between  the  fingers  and  on 
the  palm  of  the  hand,  until  its  "  stickiness  "  or  adhesiveness  ceases  to 
increase.  This  "  hand  test "  is  of  first  importance  and  in  skilful  hands 
will  largely  supersede  the  need  of  elaborate  mechanical  analysis.  It 
will  at  once  enable  the  operator  to  classify  the  soil  as  a  light  or  heavy 
loam,  clay  loam  or  clay  soil ;  it  will  show  directly  what  will  be  the  result 
of  plowing  the  land  when  wet,  the  liability  to  the  formation  of  a  plow- 

556 


APPENDIX  B. 


557 


sole,  and  whether  a  single  or  a  double  team  will  generally  be  needed  to 
cultivate  it  properly.  Also  whether  stock  can  be  allowed  to  pasture  the 
land  soon  after  rain.  Comparison  with  the  known  land  of  neighbors 
will  also  thus  become  easy,  and  in  a  measure  the  crops  best  adapted  to 
the  physical  qualities  of  the  soil,  subsoil  and  substrata,  taking  into 
account  their  respective  depths,  will  at  once  be  at  least  approximately 
determined.  The  presence  of  coarse  and  fine  sand  in  greater  or  less 
amounts  will  also  be  thus  readily  ascertained,  allowing  estimates  of  the 
percolative  properties ;  the  latter  can,  of  course,  be  more  practically 
tested  in  the  field,  in  the  manner  described  in  chapter  13,  page  242. 

A  more  definite  estimate  of  the  amount  and  kind  of  sand  present  in 
the  soil  materials  can  be  obtained  by  washing  the  kneaded  sample  into 
a  tumbler,  and  allowing  a  thin  stream  of  water  to  flow  into  it  from  a 
faucet  while  gently  stirring  the  turbid  water.  The  clay,  together  with 
the  finest  silts,  will  thus  be  carried  off  over  the  rim  of  the  glass,  and 
sand  of  any  desired  degree  of  fineness,  according  to  the  strength  of  the 
stream  of  water  used,  will  be  left  behind.  The  kind  and  amount  of 
these  sandy  materials  can  then  be  estimated,  or  definitely  ascertained 
by  weighing  or  measuring. 

This  will,  generally  speaking,  be  as  far  as  the  uninstructed  farmer  can 
readily  go ;  but  these  simple  operations  will  give  him  an  insight  into  the 
nature  of  his  soil  and  subsoil  that  will  enable  him  to  avoid  a  great  many 
costly  mistakes. 

RF.CO<;NITION  AND  MKANINC,  OK  THK  SKVKKAI,  SOIL  MINKRAI,S.' 

Those  somewhat  familiar  with  scientific  methods  and  operations,  and 
supplied  with  pocket  lens  or  microscope,  can  profitably  go  much  farther 
towards  the  definite  ascertainment  of  the  permanent  cultural  value  of 
the  land,  by  the  study  of  the  minerals  of  which  the  sand  is  composed, 
and  which  as  a  rule  represent  those  from  which  the  entire  soil  has  been 
formed  ;  therefore  indicate  in  a  general  manner  its  chemical  compo- 
sition. Such  examinations  are  specially  feasible  and  important  when 
soils  are  not  far  removed  from  their  parent  rocks,  as  in  most  of  the 
arid  region,  and  in  the  states  north  of  the  Ohio.  In  the  Southwestern 
states,  in  the  coastal  plain  of  the  (iulf  of  Mexico,  the  original  soil 
minerals  have  usually  been  too  far  decomposed  to  admit  of  definite 
identification.  Sand  is  there  as  a  rule  made  up  of  quart/  grains  of 
many  varieties,  with  only  an  occasional  tourmaline  and  pyroxene. 

Among  the  prominent  soil  minerals,  quartz  is  almost  always  recogniz- 

1  For  more  details  see  chapters  3  and  4. 


558  APPENDIX  B. 

able  by  its  glassy  luster  and  the  irregular  fracture — absence  of  definite 
planes  or  facets  of  cleavage,  causing  the  grains  to  be  abraded  or  rounded 
nearly  alike  in  all  directions.  The  feldspars :,  on  the  contrary,  always  show 
a  tendency  to  cleave  into  fragments  having  definite,  obviously  oblique 
angles,  which  are  perceptible  even  when  the  grains  are  somewhat  worn  ; 
because  of  the  difference  in  the  ease  with  which  wear  takes  place  in  the 
several  directions.  Potash  feldspar,  moreover,  which  is  the  most  im- 
portant to  be  recognized  because  it  indicates  a  relatively  large  supply 
of  potash  in  the  natural  soil,  is  but  rarely  glassy  in  luster,  but  mostly 
dull  white,  or  reddish-white. — The  lime  and  lime-soda  feldspars  rarely 
show  as  definite  forms,  because  of  their  tendency  to  form  complex 
crystalline  aggregates  (twins)  :  and  their  definite  recognition  requires 
somewhat  complex  (polarizing)  appliances  in  connection  with  the  mi- 
croscope. In  such  cases,  however,  the  accompanying  minerals  (horn- 
blende, pyroxene,  mica  and  others)  often  afford  valuable  indications, 
because  of  their  known  association  with  soda-lime  feldspars  in  certain 
rocks. 

An  abundant  occurrence  of  hornblende  fragments,  characterized  by 
their  flat,  tabular  form,  and  bottle-green  or  black  tint,  indicate,  almost 
always  a  fairly  good  supply  of  lime  in  the  soil,  but  leaves  the  potash- 
supply  in  doubt.  Pyroxene  (distinguished  by  its  smooth,  polished  sur- 
face from  the  angularly-weathering,  usually  rusty  hornblende  fragments) 
rarely  occurs  with  potash  feldspar;  and  soils  strongly  charged  with  it 
are  mostly  poor  in  potash. 

Mica  occurs  in  so  many  rocks  and  is  of  so  little  consequence  as  a 
soil— ingredient  from  the  chemical  point  of  view,  because  of  its  difficult 
decomposition,  that  its  presence  can  mostly  only  serve  to  corroborate 
or  contradict  conclusions  as  to  the  derivation  of  a  soil  from  some  par- 
ticular rock  or  region.  But  mica  serves  a  good  purpose  in  improving 
the  tilling  qualities  of  soils.  Its  thin  scales  must  not  be  mistaken  for 
the  tabular  fragments  of  hornblende. 

Calcite  in  its  several  forms  is  mostly  easily  recognized  both  by  its 
form  under  the  microscope,  and  by  the  effervescence  its  granules  show 
when  touched  with  an  acid.  This  effervescence  can  generally  be  ob- 
served on  touching  the  wetted  soil  with  chlorhydric  acid,  so  soon  as  the 
content  exceeds  two  per  cent ;  but  something  depends  upon  the  size  of 
the  grains,  as  when  these  are  very  small,  the  giving-off  of  gas  is  less  readily 
noted.  To  facilitate  it,  the  wetted  soil  may  be  warmed  before  touch- 
ing it  with  the  acid.  The  recognition  of  the  presence  of  lime  carbon- 
ate in  soils  is  so  important  as  to  justify  considerable  trouble  in  render- 
ing it  definite.  When  the  aid  of  a  chemist  cannot  be  commanded, 


APPENDIX  B. 


559 


fairly  definite  conclusions  may  be  drawn  from  the  character  of  the 
native  vegetation  ;  regarding  which,  detailed  information  may  be  found  in 
Parts  III  and  IV  of  this  volume.  But  where,  as  in  the  arid  region,  this 
criterion  is  not  available,  since  the  controlling  factor  there  is  the  mois- 
ture supply,  a  presumption  may  be  gained  by  the  application  of  a  slip 
of  moistened  red  litmus  paper  to  the  wetted  soil.  Should  the  red 
paper  be  turned  blue  within  one  or  two  minutes  it  would  indicate  the 
presence  of  carbonate  of  soda  ("  black  alkali ")  as  well  as  of  lime  car- 
bonates :  but  if  blued  only  after  twenty  minutes  or  more,  it  would  indicate 
the  presence  of  the  carbonates  of  lime  and  magnesia.  If  not  changed 
at  all,  the  conclusion  would  be  that  either  lime  carbonate  is  in  very 
small  supply,  or  that  the  soil  is  in  an  aci  1  condition.  (See  chapter  8, 
p.  122). 

Saline  and  Alkali  Soils. — The  presence  of  an  unusual  or  injurious 
amount  of  soluble  salts,  as  in  the  case  of  seacoast  and  alkali  soils,  is 
commonly  easily  ascertained  in  the  field ;  where,  if  the  surface  soil  is 
at  all  seriously  contaminated  with  soluble  salts  of  any  kind,  these  may 
be  seen  on  the  surface  during  a  dry  season,  forming  a  whitish  efflores- 
cence, which  in  most  cases  is  definitely  crystalline.  In  doubtful  cases 
a  tablespoonful  of  the  surface  soil  may  be  leached  with  water,  and  the 
first  ten  or  fifteen  drops  caught  in  a  clean,  bright  silver  spoon  and 
evaporated.  Or  the  soil  may  be  stirred  up  with  about  twice  its  bulk  of 
water  and  the  mixture  be  allowed  to  clear  by  settling,  then  evaporating. 
A  slight  whitish  film  will  almost  always  remain  in  the  spoon ;  but  if  the 
amount  be  somewhat  considerable,  the  presence  of  soluble  salts  is  very 
readily  recognized  by  pouring  a  few  drops  of  clear  water  on  one  side  of 
the  spot,  and  then  allowing  it  to  flow  gently  over  the  spot  to  another 
place,  where  it  is  again  slowly  evaporated.  Any  considerable  amount  of 
salts  present  will  be  shown  both  in  the  diminution  of  the  original  spot, 
and  in  the  soluble  residue  accumulated  where  the  water  was  List 
evaporated.  Should  common  salt  be  present  to  any  considerable  extent, 
the  residue  in  the  silver  spoon  will,  if  the  last  drops  be  allowed  to 
evaporate  slowly,  show  square  or  cubical  crystals  to  the  naked  eye,  and 
certainly  to  a  common  pocket  lens.  The  residue  may  also  be  tested 
with  red  litmus  paper  for  carbonate  of  soda,  which  would  quickly  turn 
it  blue. 

More  detailed  examination  requires  chemical  reagents  and  experience, 
but  the  above  tests  should  be  sufficient  to  prevent  the  mistaking  of 
mere  white  spots,  whose  humus  has  been  destroyed  by  fermentation 
caused  by  bad  drainage,  with  true  alkali  caused  by  excess  of  soluble 
salts ;  a  mistake  not  uncommon  in  both  the  arid  and  humid  regions. 


APPENDIX  C. 

SHORT  APPROXIMATE  METHODS  OF  SOIL  EXAMINATION 
USED  AT  THE  CALIFORNIA  EXPERIMENT  STATION. 

BY    R.    H.    LOUGHRIDGE. 

THE  California  Experiment  Station  has  for  many  years  given  the 
farmers  of  the  State  the  privilege  of  having  their  soils  examined  to  as- 
certain any  physical  defects,  deficiency  in  plant-food,  or  the  presence 
of  alkali  salts.  They  have  quite  generally  taken  advantage  of  this,  and 
the  number  of  samples  of  soil  sent  in  each  year  has  been  very  large. 

A  complete  analysis  of  a  soil-sample  requires  fully  15  days;  hence 
the  necessity  of  adopting  some  quick  methods  for  the  determination  of 
the  main  elements  of  fertility,  viz.,  humus,  lime,  potash,  and  phosphoric 
acid,  that  would  at  the  same  time  give  results  sufficiently  accurate 
for  practical  purposes.  Similarly  for  alkali  salts  in  the  soil ;  the  leach- 
ing-out  and  analysis  of  which  often  occupies  more  than  a  week. 

The  following  methods  have  been  adopted,  which  shorten  the  time 
of  examination  for  the  plant-food  of  a  soil  to  about  one  hour,  except 
for  potash,  which  requires  a  much  longer  time.  For  alkali  salts  the 
time  is  reduced  to  two  days,  and  less  if  a  pressure  filter  be  used. 

Humus. — The  Grandeau  method  of  ammonia  extraction  requires  the 
removal  of  the  lime  and  magnesia  with  weak  hydrochloric  acid,  wash- 
ing out  of  the  acid  and  then  digestion  with  weak  ammonia  ;  all  of  which, 
with  a  soil  rich  in  humus,  may  require  many  days,  though  a  number  of 
samples  may  be  put  through  at  the  same  time. 

The  method  adopted  to  determine  adequacy  or  inadequacy  of  the 
humus  (for  this  is  all  that  is  intended  in  this  examination)  is  completed 
in  less  than  half  an  hour.  It  is  based  on  the  color  of  the  humus-extract 
and  avoids  the  necessity  of  removal  of  the  lime  from  the  soil. 

The  soil  is  pulverized  in  a  mortar  with  a  rubber  pestle,  and  passed 
through  a  half-millimeter  sieve.  Seven  grams  of  the  fine  earth  is  placed 
in  a  test  tube  with  15  or  20  cc.  of  a  ten  percent  solution  of  caustic 
potash  and  boiled  for  ten  or  fifteen  seconds,  then  allowed  to  settle. 
The  humus  is  dissolved  and  the  density  of  the  color  of  the  solution  is 
an  indication  of  adequacy  or  inadequacy.  A  dense  black,  non-trans- 

560 


APPENDIX  C.  561 

lucent  solution  shows  the  presence  of  at  least  one  per  cent  of  humus 
in  the  soil ;  a  deep  brown  translucent  color  indicates  about  one-half  of 
one  percent ;  while  a  light  brown  color  clearly  shows  a  deficiency  in  the 
soil,  and  a  need  of  a  good  green-manure  crop. 

Lime. — Two  grams  of  fine  earth  is  treated  with  a  little  hydrochloric 
acid,  boiled  for  a  few  seconds,  and  ammonia  is  added  to  precipitate 
the  iron  and  alumina ;  the  whole,  with  the  soil-residue,  is  quickly  thrown 
on  a  filter  to  separate  the  mass  from  the  lime  solution,  and  washed. 
After  adding  ammonium  chlorid  the  lime  is  precipitated  with  oxalate 
of  ammonia,  and  its  adequacy  for  soil-fertility  judged  of  by  the  turbid- 
ity of  the  solution,  or  the  bulk  of  the  precipitate.  Or  the  latter  may 
be  filtered  off,  dried  and  weighed.  We  thus  obtain  a  measure  of  the 
carbonate  and  humate  of  lime  present,  by  comparing  it  with  the  pre- 
cipitate obtained  from  a  soil  whose  percentage  of  lime  has  been  cor- 
rectly ascertained. 

Potash. — The  determination  of  potash  in  the  soils  requires  more  time 
than  either  of  the  other  ingredients,  and  is  more  rarely  made  by  us. 
Our  knowledge  of  the  soils  of  the  State  of  California  obtained  through 
mvny  analyses,  gives  us  a  clue  to  those  localities  where  potash  would 
probably  be  deficient,  as  well  as  to  those  whose  soils  are  generally  ex" 
tremely  rich  in  potash  ;  the  percentages  reaching  usually  from  .5  to  as 
much  as  1.5  percent  and  more. 

For  the  determination,  two  grams  of  the  fine  earth  is  digested  in 
hydrochloric  acid  over  a  steam  bath  for  two  days,  the  insoluble  residue 
filtered  off,  the  filtrate  evaporated  to  dryness  to  render  the  silica  in- 
soluble, again  filtered  and  the  iron,  alumina  and  lime  removed  by  pre- 
cipitation with  ammonia  and  oxalate  of  ammonia  and  filtration.  The 
filtrate  is  then  evaporated  to  dryness,  the  ammonia  salts  destroyed  with 
aqua  regia  or  driven  off  by  heat,  and  the  alkalies  changed  to  chlorids. 
Any  residue  is  then  filtered  off  and  platin-chlorid  added  to  precipitate 
the  potash,  which  is  separated  and  determined  in  the  usual  way,  either 
by  reduction  of  the  platinum  by  ignition,  or  by  measurement  in  a 
Plattner's  potash  tube. 

Phosphoric  AciiL — The  determination  of  phosphoric  acid  is  based  on 
the  volume  of  the  phospho-molybdate  precipitate  in  a  tube  made  like 
a  Plattner's  potash  tube,  but  having  a  wider  interior  diameter  for  the 
smaller  portion  (not  greater  than  3  millimeters),  and  a  length  of  50 
mm.  With  this  diameter,  one  mm.  in  height  of  the  precipitate  obtained 
by  our  short  method  indicates  one  one-hundredth  of  one  per  cent  of 
phosphoric  acid  in  the  soil.  The  unit  of  measure  must  be  obtained  for 
36 


562  APPENDIX  C. 

each  tube,  unless  of  uniform  diameter,  and  is  ascertained  by  taking  a 
soil  whose  phosphoric-acid  percentage  has  been  determined  gravimet- 
rically  and  giving  it  the  following  quick  treatment;  which  must,  of 
course,  be  closely  followed  in  each  soil  to  be  examined : 

Two  grams  of  the  fine  earth  is  ignited  in  a  platinum  dish  to  destroy 
the  organic  matter,  transferred  to  a  test-tube  containing  5  cc.  of  nitric 
acid  and  made  to  boil  for  only  a  couple  of  seconds,  thus  preventing  the 
solution  of  silicates  to  any  material  extent.  It  is  not  allowed  to  stand, 
but  a  little  water  is  immediately  added  and  it  is  quickly  thrown  on  a 
small  filter  and  washed  with  a  little  water.  The  phosphoric  acid  is  then 
precipitated  with  molybdic  acid  at  the  proper  temperature ;  allowing  it 
to  settle,  the  liquid  is  drawn  off  and  the  precipitate  transferred  to  the 
measuring- tube.  It  settles  into  the  small  part  in  a  short  time  if  the 
latter  is  not  too  narrow,  and  is  then  measured  with  a  millimeter  scale. 
This  represents  the  percentage  as  found  in  the  soil  by  the  gravimetric 
method,  and  serves  as  a  guide  for  other  examinations,  whose  agreement 
with  gravimetric  determinations  is  generally  quite  close,  and  quite  suf- 
ficient for  practical  purposes.  The  rapidity  with  which  the  solution  is 
made  and  separated  from  the  soil  is  a  matter  of  special  importance  for 
comparative  results,  or  determination  of  percentages ;  for  if  the  acid 
solution  be  allowed  to  stand  for  some  time  before  filtration  from  the 
soil,  silica  passes  into  solution  also,  and  the  volume  of  the  molybdate 
precipitate  is  increased  by  it ;  thus  vitiating  the  results  and  adding  to 
the  time  required  for  the  method.  By  this  short  method  the  practically 
important  phosphoric  acid  in  the  soil  may  be  approximately  deter- 
mined within  half  an  hour. 

SHORT   METHOD    FOR   ALKALI    SALTS. 

The  old  method  of  obtaining  solutions  of  the  salts  by  leaching  the 
soil  on  a  filter  until  all  of  the  alkali  had  been  washed  out  has  been 
replaced  by  the  following  short  one.  50  or  100  grams  of  the  well- 
mixed  soil  is  placed  in  a  bottle  containing  200  cc.  of  water,  shaken  up 
occasionally  during  12  hours  and  allowed  to  settle.  The  solution  may 
then  be  passed  through  a  common  filter  (or  preferably  a  pressure  filter) 
and  an  aliquot  part  (usually  50  cc.)  of  the  filtrate  evaporated  to  dry- 
ness  in  a  platinum  basin  and  ignited  at  a  temperature  just  below  redness 
to  destroy  any  organic  matter  that  may  be  present.  The  basin  and 
contents  are  weighed  and  the  soluble  salts  are  dissolved  in  a  very  little 
water  and  separated  by  filtration  through  a  small  filter  into  a  50  cc. 
cylinder  and  the  alkali  carbonates  and  chlorids  determined  by  titration, 
being  calculated  as  sodium  compounds. 


APPENDIX  C.  563 

The  material  remaining  on  the  filter  and  in  the  basin,  consisting  of 
insoluble  earth,  carbonates  and  calcium  sulfate,  is  gently  ignited  in  the 
basin  and  weighed ;  the  difference  between  this  and  the  first  weight 
gives  approximately  the  total  soluble  salts,  which  should  substantially 
correspond  to  the  titrations  made. 

The  sulfates  are  determined  by  differences  between  these  and  the 
total  alkalies.  The  solution  may  contain  some  sulfate  of  magnesia,  or 
calcium  and  magnesium  chlorids,  and  these  are  determined  gravime- 
trically. 

Nitrates,  which  may  have  been  destroyed  in  the  first  ignition,  are 
determined  in  the  original  solution  by  the  picric  method.  Any  mag- 
nesia rendered  insoluble  by  the  ignition  may  usually  be  accounted  for 
as  chlorid,  unless  much  nitrate  is  present  which  is  rarely  the  case  in 
carbonated  alkali.  If  much  nitric  acid  was  found,  it  should  be  first 
assigned  to  magnesia. 


INDEX. 


A. 

PAOB 

Absorption  and  movements  of  water  in  soils 221 

of  solids  from  solutions 267 

of  gases  by  soils 272,  275 

Acacias,  tolerance  of  alkali 480 

Accessory  minerals 50 

Acid,  strength  used  in  soil  analysis 341 

Acidic  and  basic  eruptive  and  metamorphic  rocks 49 

Acidity,  neutrality,  alkalinity  of  soils 322 

Acids  of  different  strengths,  analysis  with  ;  table 326,   341 

Action  of  plants  in  soil  formation,  mechanical  and  chemical 19 

Aeration  and  reduction  as  influencing  nitrification 147 

effects  of  insufficient,  in  soils 2.So 

excessive,  injury  in  arid  regions 2  So 

^robic  and  anerobic  bacteria 144 

Air,  functions  in  soils 279 

"     of  soils,  composition  of 2 So 

Air-space  in  soils  ;  figure 108 

Alabama,  vegetation  and  soil-characters 511 

Alaska  current,  effects  on  California  climate 296 

Alinit 149 

Alkali  carbonates  and  snlfates,  inverse  ratio J5I,  452 

carbonates,  effects  on  clay 62 

effects  on  culture-  plants  ;  figure 426,  427 

Alkali-heath,  range,  tolerance  of  alkali,  figure 544,  545 

Alkali  lands,  crops  for  strong jf>S 

effects  of  irrigation  on jrS 

efficacy  of  shading 157 

exceptionally  productive  when  reclaimed jS^ 

fertilization  not  needed  in }S^ 

formation  from   leachings  of  slopes 15,; 

geographical  distribution  of 423 

high  and  lasting  production  when  reclaimed }Sj 

inducements  toward  reclamation  of 4Si 

in  the  San  Joaquin  valley,  Cal.,  figure ,    425 

possible  injury  to,  from  excessive  leaching 462 

565 


566  INDEX. 

PACK 

Alkali  lands,  summary  of  conclusions 453 

surface  and  substrata  of 429 

utilization  and  reclamation  of 455 

of  world-wide  importance.  .......  c 424 

vegetation  of 534 

Alkali-resistant  crops „ 455 

Alkali  salts,  black  and  white 441 

composition  of 439 

composition  of  ;  general  table 442,  443 

distribution  in  heavy  lands 436,  437 

effects  on  beet  crop 465 

horizontal  distribution  of 439 

in  hill  lands 439 

in  sandy  lands 433,  435 

in  Salton  Basin,  distribution  of 436,  438 

leaching-down  of 459 

nature  of 423 

plant  food  in 441,  444 

reactions  between 449,  450 

reduction  by  cropping 463 

relative  injuriousness  of 464 

removal  from  the  soil 458 

removal  by  deep-furrow  irrigation  ;  figure 460,  461 

tolerance  of  various  crop  plants  ;  table 466,  467 

total  in  lands  ;  estimation  of 444 

underdrainage  the  universal  remedy  for 460 

upward  translocation  from  irrigation 433 

vertical  distribution  in  soils 429,  431,  432,  434 

Alkali  soils  and  seashore  lands 422 

calcareous  character  of 28 

composition  of,  as  a  whole 445,  446,  447 

how  native  plants  live  in 430 

origin  of 422 

repellent  aspect,  cause  of 424 

retention  of  silica  in 392 

Alkali  spots,  white 286 

Alkali,  rise  of 428 

turning  under  of  surface 456 

weeds  as  cattle  food   468 

study  of,  by  Loughridge  and  Davy 535 

Aluminic  hydrate,  in  soils  of  California  and  Mississippi ;  table 101,  390 

Alluvial  soils 12 

Ammonia-forming  bacteria 149 

Ammonia  gas,  absorption  of,  by  soils  ;  figure  274,  275 

Ammonic  carbonate,  effects  on  glass 18 

Ancient  civilizations,  preference  for  arid  countries 417 

rare  in  humid  countries 418 

Apatite 63 


INDEX.  567 

PAGB 

Arid  and  humid  climates,  rock-weathering  in 47 

Arid  and  humid  regions,  criteria  of  soils  of 371 

contrast  between  soils  of 28 

soils  of 1 1 1,  371 

Arid  and  humid  soils,  general  comparison  ;  table 375,  377 

Arid  belts,  subtropic 298,  299 

utilization  of 299 

Arid  conditions,  local,  in  tropical  countries. 401 

Aridity,  influence  upon  civilization. 417 

Arid  region,  bunch  grasses  on  soils  of , in 

standing  hay  in 300 

upland  soils  of  ;  table 373,  374 

Arid  soils,  productiveness  induces  permanent  civil  organization 412 

Arroyo  Grande  and  Yazoo  buckshot  soils 345 

Asparagus,  resistant  to  salts 475 

Atmosphere,  composition  of  ;  table 16 

Azotobacter 1 56 

Liprnan  on 156 

B. 

Bacteria,  active  in  soil-formation 20 

aerobic  and  anaerobic 144 

denitrifying 148 

food  and  functions  of 145 

in  soils,  numbers  of 142 

micro-organisms  of  soils 142 

multiplication  of J44 

nitrifying 146 

Bacterial  life,  effect  on  soil,  condition 149 

relation  of  carbonic  dioxid  to 281 

Bacteroids 151 

Mork  figures 152,  153 

Basaltic  rocks 49 

Basalts,  red  soils  from 52 

Basic  slag 64 

Basin  irrigation,  advantages  of 243 

Bauxite  in  soils 101,390 

Beet,  sugar,  effects  of  salts  on 474 

tolerant  of  common  salt 474 

Bhil  soils 4M 

Bicarbonate  of  soda 7$ 

Black-alkali  lands,  difficulty  in  draining 462 

neutralizing  of 457 

waters,  use  of 250 

why  so  called 78 

Black  earth  of  Russia,  humus  in  ;  table 130 

Black  sand 45 


568  INDEX. 

PACK 

Black  prairie  soils 53 

Black  soils  and  lands 283 

Blizzards  in  continental  America 298 

Blown-out  lands 9 

Blue  tint  in  clays  and  subsoils 45 

Bodengare 149,  150,  281 

Bog  ore,  formation  of,  in  subsoils 46,  66 

Bones,  composition  of 64 

Bone  meal,  efficacy  of ...     65 

Borax,  borate  of  soda 79 

Bottom  water 227 

rise  of,  from  irrigation 227,  230 

Bottoms,  first  and  second,  contrast  between 506,  507,  509 

Bottoms,  first,  tree  growth  of 507,  509 

Brahmaputra  alluvium,  Assam 413 

Brown  iron  ore , 44 

' '  Buckshot  "  soils  of  Yazoo  bottom «. 1 16 

"  Bunch  grasses  "  as  alkali-resistants 471 

Burning-out  of  humus,  effects  of 118 

Burrowing  animals,  work  in  soil-formation 160 

C. 

Calcareous  clay,  crumbling  on  drying 1 16 

formations,  predominance  in  Europe 525 

soils,  definition  of . .  .367,  496,  524 

solubility  of  alumina  and  silica  in 389 

subsoils,  and  hardpans 162 

Calciphile,  calcifuge  and  silicophile  plants , 521 

Calcite,  calcareous  spar 39 

recognition  of 39 

Caliche,  in  Chile,  Nevada,  and  California 66,  67 

Capillarity 189 

Capillary  water,  reserve  of 229 

rise  of 202  to  207 

Carbonated  water,  action  on  feldspar 32 

action  on  silicates 18 

universal  solvent 17 

Carbonate  of  soda 77 

injury  to  soils  and  plants 78 

Carbonates,   chlorids    and  sulfates    of    earths  and    alkalies,    reactions 

between 449,  450 

Carbonic  acid , 17 

secreted  by  roots 20 

Carbonic  dioxid,  absorption  of,  by  soils 274 

heavily  absorbed  by  ferric  and  aluminic  hydrates. . . .  278 

occurrence,  formation , 17 

relation  to  fungous  activity 281 


INDEX. 


569 


PAGE 

Cascade  range,  climatic  divide  in  N.  \V.  America 297 

Caves  in  limestone  regions 41 

Celery,  moderate  tolerance  of  alkali 475 

Centrifugal  elutriator,  Voder's 92 

Cereals,  alkali-resistance,  barley,  gluten  wheats  471 

Channels,  cutting-out  by  gravel 6 

Charcoal,  absorption  of  gases  by 276,  277 

Chemical  absorption  by  soils 270 

action  of  roots 20 

analysis  of  soils  (in  general) 323 

character  of  soil,  recognition  of 322 

decomposition,  causes  intensifying 21 

processes  of  soil  formation 16 

Chile  saltpeter 66 

Chernozem 1 30 

analyses  of,  table 364 

Chestnut,  American,  a  calcifuge  tree 491,  519 

Chlorin,  largest  ingredient  of  sea  water 27 

Chlorite 36 

Chlorosis  of  vines  in  marly  lands 526 

Churn  elutriator,  Hilgard's  ;  figure 91 

Circling  of  hill  lands 220 

Citrus  fruits,  injury  to,  from  alkali 478 

lemons  most  sensitive 4/8 

sensitiveness  to  common  salt 477 

Classification  of  rocks 47 

of  soils 10 

Clay  as  a  soil  ingredient 83 

colloidal 59 

functions  of,  in  soils 59 

maintains  crumb  structure 1 10 

Clays,  claystones,  clay  shales 48 

colors  of  58 

formation,  flocculation  and  deposition  of 33 

maturing  of 60 

plasticity  and  adhesiveness,  influence  of  fine  powders  on 85 

influence  of  ferric  hydrate  on 85 

Clay -sandstones,  soils  from 57 

Clays,  separation  of,  by  subsidence,  by  centrifuge 89 

varieties,  enumeration  of,  and  characters 57,  58 

fusibility  of 5^ 

Claystones,  soils  from 59 

Cleavage  of  rocks 3 

Cleopatra's  needle 2 

Climate 287 

Climatic  and  seasonal  conditions 21 

Climates,  continental,  coast  and  insular 297 

Coffee  soils,  calcareous 4 '  7 


570  INDEX. 

PACK 

Colloidal  clay,  amount  in  soils.    Table 84 

analysis  of,  by  Loughridge 385 

effects  of  alkali  carbonates  upon 62 

investigation  by  Schlcesing 59 

properties  of ..  61 

separation  of,  by  boiling  and  kneading 61 

Colloid  humates 133 

Colluvial  soils : . . .  12 

Colors  of  soils,  advantages  of 283 

Common  salt,  injuriousness  in  soils 76 

recognition  of 76 

removal  from  soils 76 

Conglomerates 48 

Conifers,  tall  growth  of,  in  arid  regions 517 

Contraction  of  soils  in  wetting  and  drying 1 14 

Co-operation,  favored  by  need  of  irrigation.   419 

Corsican  and  maritime  pine,  ash  analyses 520 

Cotton,  compact  growth  and  heavy  boiling  on  calcareous  soils 503 

Cracking  of  clay  soils  in  drying 113 

Cressa  ;  range,  tolerance  of  alkali,  figure 545,  546 

Creep 12 

Crops,  alkali-resistant 455 

Crumbling  of  calcareous  clays  on  drying 1 16 

Crumb-structure  of  soils  ;  figure no 

Crusting  of  soils,  effects  of 111,117,  221 

Cultivated  soils,  analysis  of , 325 

investigation  of 316 

Cultural  experience  the  final  test 324 

Cutting-out  of  channels  by  water-borne  gravel 6 

Cypress,  different  forms  of  ;  figures 507,  508 

D. 

Date  palm,  resistance  to  alkali 47& 

Decomposition,  chemical,  of  rocks 16 

Decolorizing  action,  of  soils,  charcoal 267 

Deep-rooting  of  native  plants  in  arid  region 174 

Deforestation,  effects  of 2I9 

Deltas,  formation  of 7 

Denitrifying  bacteria T48 

Deserts,  effects  of  winds  in ' 8 

Desert  sands,  only  lack  water  to  become  productive 420 

Dew,  formation  of 3°7 

rarely  adds  moisture  to  soils 3°^ 

within  the  soil 3°^ 

Differentiation  of  soil  and  sub-soil,  causes  of 121 

Distance  between  furrows  and  ditches 241 

Dolomite..  42 


INDEX. 


571 


Drainage,  rights-of-way  for 461 

Drainage  waters,  use  for  irrigation 250 

Drain  waters,  analyses  of,  table 22 

leaching  effects  of 271 

Drouth,  resistance  to,  in  arid  soils 167 

Dust  soils,  nature  of 104 

slow  penetration  of  water  in 105 

Dust  storms 9 

Dynamite,  used  for  shattering  dense  substrata 181 

Earth's  crust,  known  thickness xxix 

Earthworms,  action  of  in  soil-formation 158 

Ecological  studies 314 

Egypt,  obelisks  of 2 

Elements  constituting  earth's  crust,  table  of xxix 

important  to  agriculture,  list  of xxxi 

Elutriator,   Hilgard's,  figure 91 

Epsomite,  epsom  salt,  in  soil 78 

Eremacausis 1 29 

Erosion  in  arid  regions 219 

in  Mississippi  table  lands  ;  figures 218 

lowering  of  land  by 15 

of  rocks  by  sand  ;  figure 10 

Eruptive  rocks,  basic  and  acidic 49 

rocks,  soils  from 52 

Eucalyptus,  tolerance  of  alkali 480 

European  observations  on  plant  distribution 519 

standards  of  plant-food  adequacy — Maercker's  table 369 

Europe,  predominance  of  calcareous  formations  in 525 

Evaporation  and  crop  yields,  calculated 193 

and  crop  yields,  observed  ( Fortier) 194 

and  plant  growth 193 

counteracting,  in  alkali  lands  455 

dependence  on   air    temperature ;    Fortier's   experiments, 

table 255 

from  reservoirs  and  ditches 257 

from  water  surfaces 254 

wet  and  moist  soils 254 

in  different  climates 192,  256 

in  different  localities,  California 255 

restrained   by   loose   surface    layer ...  255 

through  roots  and  leaves,  amount  of 262,  263 

Expansion  by  oxidation 18 

F, 

Farmyard  or  stable  manure 72 

Feldspars,  weathering  of 31 

products  of 32 


572 


INDEX. 


Ferghana,  alkali  lands  in 441 

Ferric  hydrate,  effects  of IOQ 

functions  of,  in  soils.    285 

high  absorptive  power  of 277 

in  Hawaiian  soils  ;  table ...    356 

more  diffused  in  humid  than  in  arid  soils 392 

Ferric  phosphate,  unavailability  of 356 

Ferroso-ferric  hydrate  and  oxid 18,  45 

Ferrous  oxid 18 

Ferruginous  lands,  injury  from  swamping  of 233 

Fertilizers,  mineral 63 

waste  of,  by  leaching 269 

Flocculation  and  floccules 91 

Flocculated  structure  ;  cements  maintaining no,  in 

Flood-plains  of  rivers 14,  15 

Fool's  gold 75 

Force  exerted  by  roots 19 

Forecasts,  general,  of  soil  quality  in  forest  lands 507 

of  soil  values,  popular 313 

Forest  trees,  forms  of 499  to  502 

of  Atlantic  states  on  alkali  lands 481 

Form  and  development  of  trees,  differences  in 498 

Forms  of  leaves,  variation  in 502 

black-jack  oak 499,  501 

post  oak 499,  500 

trees,  deciduous,  in  arid  region 516 

willow,  scarlet,  black  and  Spanish  oaks 502 

Freezing  water,  effects  of 3 

Frost,  effect  of  soils , 1 18 

Fruiting,  favored  by  lime  in  soils  503 

Fungi  and  molds,  action  of  123 

functions  in  humus-formation 1 57 

G. 

Gases,  absorption  of,  by  soils 272,  275 

partial  pressure  of    276 

Germination  of  seeds 309 

Glacier  flour,  fineness  and  fertility  of 5 

physical  analysis  of 5 

Glaciers,  grinding  and  abrasion  by  ;  figure 3 

Glauber's  salt 77 

Glauconite,  in  calcareous  sandstones 56 

Gneiss  soils 51 

Gobi  desert,  migration  of  lakes 9 

Going-back  of  orchards 182 

Grain-sizes,  effect  on  percolation  ;  table 224 

influence  on  soil  texture 100 


INDEX. 


573 


PAGE 

Grandeau  method  of  humus  estimation 132 

Granite  soils,  potash  and  phosphoric  acid  in 50 

Granitic  rocks,  weathering  of 47 

sand,  formation  in  arid  climates 2 

Grano-diorite  soils,  of  Sierra  Nevada 51 

Granular  sediments,  influence  upon  tilling  qualities 102 

Grape-vine,  alkali,  tolerance  of 475 

Grasses,  cultivated,  sensitive  to  alkali 471 

Greasewood,  range,  tolerance  of  alkali  ;  figure. 542,  543 

Greenstones,  soils  from 51 

Ground  water,  depth  most  favorable  to  crops 228 

variation  of  surface  of 228 

Gulf-stream 295 

Gypsum  or  selenite,  formation  from  sea-water  evaporation 42 

how  recognized 42 

H. 

Halite 76 

Hardpans,  causes,  formation  and  cements  of 185 

Hardpan,  physical,  analysis  of 103 

plowsole  .  .      24 1 

Hawaiian  Islands,  humid  and  arid  sides  of 297 

soils,  analyses  of 356 

Hay  bacillus  ;  figure 149,   150 

Heat  and  cold,  effects  on  rocks I 

of  high  and  low  intensity 304 

reflection  and  dispersion  from  soil  surface 304 

relations  to  soils  and  plant  growth 301 

trapping  of  suns 288 

Heaviest  clay  soils,  physical  analysis  of 115 

Heaving-out  of  grain 119 

Hematite ....     44 

Herbaceous  plants  as  soil  indicators , 517 

Hog-wallows 114 

Hornblende  and  pyroxene 33 

weathering  of 33 

Horsetail  rushes,  secretion  of  silica  by 31 

I  Inmates  and  ulmates 133 

cementing  effects  of ill 

Humid  and  arid  climates,  rock-weathering  in 47 

Humid  region,  upland  soils  of  ;  table 3/2,   374 

Humification  in  soils 20 

normal  conditions  of 1 29 

tests  ;  Snyder,  tables 140 

Hutnin  substances,  formation  of 1 23 

Humus,  ainidic  constitution  of 125 

and  coal,  amountsof.from  vegetable  substance 128 


574  INDEX. 

PACK 

Humus,  amount  in  soils 133 

ash  of,  from  Minnesota  soils,  analysis 134 

decrease  of  nitrogen-content  with  depth ,  135 

determination  in  soils 132 

distribution  in  the  surface  soil 157 

functions  in  soils .    21 

in  arid  and  humid  regions 138 

in  black  earth  of  Russia 130 

in  Minnesota  soils 131 

in  North  Dakota  soils 133 

in  the  surface  soil 120 

losses  from  cultivation  and  fallow 131 

nitrogen  of 124,  135 

percentage  in  soils,  and  nitrogen-content  of,  tables. .  .135,  136,  137 

porosity  of 124 

progressive  changes  in  soils 126 

relation  to  bacterial  content 144 

scanty  in  arid  soils,  but  rich  in  nitrogen 397 

substances,  physical  and  chemical  nature  of 124 

variation  of,  with  original  materials 139 

volume  weight  of,  table 125 

versus  adipocere 140 

Hydraulic  elutriation 90 

Hydro-mica 35 

Hydrous  silicates  in  soils  of  arid  region 388 

I. 

Ice-flowers  on  soils. 119 

Immediate  plant-food  requirements,  ascertainment  of 333 

productiveness,  chemical  tests  of 337 

productiveness  vs.  permanent  value  of  soils 318,  327 

India,  climatic  contrasts 401 

Indian  soils,  table  of  analyses 410,  412 

types  of  soils 411 

Indo-Gangetic  plain  ;  calcareous  hardpan,  kankar 411 

Injury  from  excessive  runoff,  prevention  of 220 

to  plants  from  the  various  salts 531 

to  soils  and  plants  from  carbonate  of  soda 78 

Insects,  work  in  soil-formation 160 

Insoluble  residue  of  soils  ;  less  in  arid  than  humid 384 

Insufficient  rainfall,  leaves  sea  salts  in  soils 28 

Insular  climate,  of  Britain,  western  Europe 298 

Introduction xxix 

Injury  from  swamping,  permanent 232 

Iron  carbonate  solution,  how  formed 44 

coloring  clays 5& 

minerals 44 

pyrites,  how  recognized. 75 


INDEX. 


575 


Irrigation,  basin,  advantages  and  disadvantages 244 

by  check  flooding 237 

flooding 237 

furrows 238 

lateral  seepage 242,  241 

shallow,  deep  and  wide  furrows  ;  diagram 239 

surface  sprinkling 237 

underground  pipes 245 

ditches,  leaky,  effects  on  alkali  lands 429 

excessive  surface  rooting  caused  by 245 

methods  of 236 

necessitates  co-operation 419 

Irrigation  water,  abundant  use  of  saline 249 

duty  of 25 1 

economy  in  use  of 243 

effects  of  saline,  figures 247 

heavy  losses  in  using 252 

limits  of  salinity 246,  248 

loss  by  evaporation 252 

loss  by  percolation  ;  diagram 253 

quality  of 246 

saline,  how  to  use 249 

testing  penetration  of 242 

temperature  of 244 

Irrigation,  winter,  advantages  of 236 

Isinglass 43 

J- 

Janesville  loam,  chemical  analysis  of 331 

Japan  current 296 

Jasper  and  hornstone  pebbles,  weathering  of 30 


Kainit,  composition  of 71 

Kaolinite  and  clay  ;  kaolin 32 

assumes  plasticity  on  trituration  with  water 60 

crystalline  form  of 22,  59 

lacks  plasticity (» 

Kaolini/.ation,  results  in  zeolite-formation 395 

slow  in  arid  regions S;,  3X6 

L. 

Landholding,  units  of,  smaller  in  arid  than  in  humid  region 420 

Landlocked  lakes,  water  of 27 

Land  plaster  as  a  fertilizer  ;  effects  on  soils 43 


576  INDEX. 

FAGB 

Landslides 12 

Laterite  soils,  Wohltmann's  definition 416 

Terra  roxa  of  Brazil 416 

Leaching  of  the  land 22 

Legumes,  bacteria  of 150 

mostly  sensitive  to  alkali 472 

Leguminous  plants,  mostly  calciphile  ;  exceptions  518 

Leucite,  potash  content  32 

Lichens,  action  on  rock-surfaces , 19,     20 

Lignites  and  coal,  how  formed 127 

Lime  a  dominant  factor  in  productiveness 353 

Lime  carbonate  in  sea  water 26,  27 

removed  from  earth's  surface 41 

summary  of  effects  in  soils 379 

Lime-content,  effects  of  high,  in  soils 365 

effects  on  availability  of  phosophates,  table 366 

"  Lime-country  is  a  rich  country  " 365 

Lime,  excess  of,  in  arid  soils 378 

Lime  feldspars,  leave  lime  carbonate  in  soils 32 

in  alkali  lands  protects  plants  from  salts 532 

lands,  failure  of  tea  on 414 

Lime-loving  trees 490  to  429,  497 

Lime,  most  abundantly  leached  out 24 

percentages,  what  are  adequate 367 

in  coast-belt  soils 496,  497 

in  heavy  clay  soils  ;  table 368 

Lime  renders  lower  amounts  of  plant-food  adequate 354 

Limestone  countries 53 

,  Rotten . 54 

soils,  excluded  from  comparison  of  arid  and  humid  soils. . . .  376 

residual   53 

Limestones,  impure,  as  soil-formers 40,  53 

residual  soils  of,  how  formed 40 

soft,  or  marls.  . ; , 4o 

slow  disintegration  of  pure 63 

Limit  of  acid  action  on  soils,  investigation  of,  by  Loughridge 340 

Limonite 44 

Loamy  and  sandy  soils,  show  little  shrinkage 117 

Loose  surface  layer,  illustration  of  effect,  figure 258,  260 

prevention  of  evaporation  by 257 

Loss  of  humus  in  summer  mulch 132 

Louisiana,  vegetation  and  soil-characters 512 

Lowland  tree-growth 506 

Lysimeter 227 

M. 

Madagascar,  character  and  soils  of 405,  406 

climate  and  rocks  of 406 


INDEX. 


577 


PAGB 

Madagascar,  methods  used  by  Muntz  and  Rousseaux 406 

potash  and  lime  leached  into  valleys 407 

red  soils 407,  409 

table  of  soil  analyses 408 

Madras,  red  soils  of 415 

Magnesia,  effects  of  excess  over  lime 382 

exceeds  lime  in  tropical  soils 405 

high  in  arid  soils 381 

leached  out  next  to  lime 24 

proper  proportions  to  lime 383 

Magnesian  limestones  as  soil- formers 42 

Magnesian  soils  largely  poor 36 

Magnetite 45 

Mai/.e  and  sorghums,  alkali-resistance 471 

Maize  roots  in  humid  and  arid  region 175,  176 

Manganese,  more  in  humid  than  arid  soils 383 

stimulant  effects  on  crops 383 

Marble  and  limestones,  formation  of.  ... 39 

Marls,  gypseous  and  calcareous 43 

Marly  substrata 1 86 

Marine  saline  lands 527 

first  crops  for 533 

reclamation  for  culture 534 

Matiere  noire  ;  active  nitrification  of 132,  360 

Mechanical  analysis  of  soils SS 

Melilots,  white  and  yellow,  alkali  resistance 473 

Mesas  of  arid  region 14 

Mesopotamia,  rehabilitation  of 421 

Metamorphic  rocks 46 

Methods  of  irrigation 236 

soil  analysis 325 

Mica  as  a  soil  ingredient 35 

weathers  slowly .  35 

mistaken  for  gold  and  silver 35 

Mica-schist  soils 51 

Micro-organisms  of  soils 142 

Mineral  fertilizers 63 

ingredients  of  soils,  minor 63 

Minerals  injurious  to  agriculture 73 

major  soil-forming,  and  rock-forming,  list  of 29 

tints  of iS 

unessential  or  injurious  to  soils 75 

Mirabilite 77 

Mississippi,  changes  in  vegetation  from  east  to  west  in  northern 490 

investigations  in,  by  writer 489 

northern,  vegetative  bi-lts  in  ;  map 490 

vegetative  belts,  descriptions  of 490,  491,  492 

Mississippi  river,  sediment  carried  by 7 


578  INDEX. 

PAGB 

Mississippi,  southern,  central  prairie,  long-leaf-pine  belts 493 

coast-belt ;  pine  meadows  ;  profile 495 

live-oak  or  shell  hammocks 495 

Mississippi  valley,  climate  of 298 

Mississippi  water,  annual  variations  in 25 

generalized  composition  of 25 

Modiola,  of  Chile 469 

Moisture  hygroscopic,  table 196 

influence  of  temperature  and  air-saturation 197 

method  of  determining 197,  198 

Mitscherlich's  objections 199 

utility  to  plant  growth 199 

available  to  growing  plants 211 

distribution  in  soil,  as  affected  by  vegetation 264 

evaporated  from  forests 265 

Eucalyptus 265 

in  Russian  forests  and  steppes 265 

requirements  of  crops  in  the  arid  region 212 

l,oughridge's  tables  of  same 214 

supplied  by  tap  roots 229 

useful  to  crops  retained  by  alkali  lands 433 

wasted  by  weeds 264 

Moraines,  in  North  Central  states 5 

Mosses,  follow  lichens  in  rock  decomposition 20 

Moulds  and  fungi,  action  of 123 

Mountain  chains,  arid  climate  under  lee  of 294 

effects  of,  on  rainfall 293 

Muddy  waters 251 

Muir  glacier,  analysis  of  mud 5 

Mulches,  loss  of  humus 132 

Mulching  with  straw,  sand , 266 

Mustard  family,  sensitive  to  alkali 473 

Myrobalan  root,  use  for  grafting  in  alkali  lands 479 

N. 

Native  vegetation,  basis  of  land  values  for  farmers 488 

causes  governing  its  distribution  not  an  unsolvable 

problem 489 

result  of  struggle  for  existence 487 

Native  grasses  for  alkali  lands 470 

Native  growth,  cogency  of  conclusions  based  on 314 

New  Mexico,  soils  from  ;  analysis 378 

Nile  water,  Letheby's  analyses  of 25 

Nitrate  deposits,  origin  of.    - 67 

of  soda 66 

Nitrates,  waste  of,  by  leaching 24,  68 

Nitrification,  active  in  matiere  noire 360 


INDEX. 


579 


Nitrification  and  denitrification 145 

in  alkali  lands 68 

in  soil  of  "  ten-acre  tract." 359 

intensity  in  arid  climates, 68 

list  of  substances  favoring 147 

of  organic  matter  in  soils,  experiments 358 

not  active  in  unhumified  matter 359,  360 

Nitrifying  Bacteria 146 

Nitrobacterinm  ;  conditions  of  activity 146 

Nitrogen-absorbing  bacteria 156 

Nitrogen,  absorbed  more  abundantly  than  oxygen 278 

accumulation  of,  in  humus 1 24 

adequacy  in  humus,  lowest  limit  of 363 

in  soils 357 

availability  of,  in  soils  ;  ascertainable 363 

content  of  humus 135 

deficiency,  pot  test,  figure 362 

determination  of,  in  soils 357 

hungry  soils  ;  table 361 

percentages  in  humus,  what  are  adequate 360 

supply  of  plants,  views  on, 150 

Nitrosomonas,  figure 246 

Nodules  of  legumes 151 

North  Central  States,  herbaceous  vegetation  on  calcareous  soils  ...  .514,  515 

lowland  growth  in  uplands,  when 515 

vegetation  and  soil-character 513 

Nutritive  salts  in  alkali 44 1 

O. 

Ocean  currents,  Gulf-stream  and  Japan-stream 295  296 

Olive,  resistance  to  alkali 47>S 

Organic  and  organized  constituents  of  soils 1 20 

Organisms  influencing  soil-conditions 142 

Oxalic  acid,  secretion  by  lichens 19 

Oxidation,  expansion  by iS 

Oxids  constituting  earth's  crust  ;  table 31 

Oxygen,  action  in  weathering  rocks iS 

proportion  of,  in  earth's  crust 30 


Pamperos 9 

Peat  bogs 122 

Peaty  soil,  shrinkage 1 1 7 

Percolation  in  natural  soils  :  diagram 223,  225,   226 

rate  of,  as  influenced  by  grain-sizes 224 

Permanent  value  of  land  vs.   Immediate  productiveness 340 


580  INDEX. 

PAGR 

Physical  and  chemical  causes  of  vegetative  features 505 

conditions  of  plant  growth 319 

Physical  analyses,  correlation  with  popular  names 96 

results  of 94 

table.     Mississippi  and  California  soils 98 

analysis  of  soils 88 

constituents  of  soils 10 

Physico-chemical  investigation  of  soils 313 

Physiological  soil  analysis 333 

Phosphate  fertilizers,  importance  of 65 

Phosphate  fertilization,  in  arid  region 393 

in  California 393 

Phosphoric  acid,  limits  of  adequacy  in  soils 355 

minute  amounts  leached  from  soils 24 

no  constant  difference  between  arid  and  humid  soils. .   393 

rendered  inert  by  ferric  hydrate 355 

Phosphorites,  low-grade,  of  Nevada,  Russia 63,  64 

Plane  tree,  oriental,  resistant  to  alkali 480 

Plant-adaptation  "  varying  from  province  to  province  " 523 

Plant  associations,  plant  formations 315 

Plant  distribution,  Thurman's  physical  theory  of 519 

Plant-development  under  different  temperatures 309 

Plant-food,  accumulation  in  finest  parts  of  soils 87 

high  percentages  mean  high  land  value 346 

ingredients,  condition  of,  in  soils 319 

in  virgin  soils,  lowest  limit  of,  table 352 

limits  of  adequacy 353 

minute  amounts  may  produce  large  crops 410 

percentages,  what  are  high 34$ 

percentages,  low 346 

water-soluble,  reserve,  unavailable 32° 

Plant-growth  on  arid  subsoils 166 

Plants,  deep-rooting  in  arid  region i?4 

indicating  irreclaimable  alkali  lands 535.  53^ 

Plant  root  action,  cannot  be  imitated  in  laboratory 324 

Plasticity,  absence  of,  in  fine  powders 60 

of  clay,  causes  of 60 

lost  by  burning 60 

Plot  tests,  difficulties  and  uncertainties  of 334 

plan  of,  figure 335 

Plowsole,  how  formed,  by  shallow  irrigation 186,  241 

Poor  chalk  lands 525 

Pore-space IQ8 

Porosity  of  humus 1 24 

Port  Hudson  bluff,  lignite  in,  figure I2$ 

recession  of i  J6 

Potash,  abundant  in  arid  soils 395 

and  soda  in  arid  and  humid  region   394 


INDEX. 


58l 


PAGE 

Potashes,  production  of  detrimental  to  agriculture 69 

Potash  feldspar,  supplies  potash  to  soils 32 

fertilization  first  in  humid,  last  in  arid  region 396 

from  sea  water 69 

limits  of  adequacy  in  soils 354 

minerals,  orthoclase  feldspar 68 

preferential  retention  of,  in  soils 272 

Salts,  Stassfurt 69 

slightly  leached  out 24 

sulfate,  high-grade yr 

Pot-culture  tests 336 

Powders,  absorption  of  various  gases  by,  table 277 

Prairie  soils,  black 53 

Preparation  of  soils  for  physical  analysis 89 

Productive  capacity  and  duration,  forecast  of 346 

Progress  of  humification  and  formation  of  coal,  table 126,  127 

Pulverulent  soils  of  arid  regions 87 

Purifying  action  of  soils 269 

Putrefactive  processes,  relation  to  carbonic  gas  and  amerobic  bacteria. .  282 

Putty  soils 103 

Pyroxene,  augite , 33,  34 

Q- 

Qualifications  required  for  soil  study 524 

Quality  of  irrigation  water   246 

Quince,  resistance  to  alkali 479 

Quartz  and  allied  rocks .  .  29 

sand  most  prominent  ingredient  of  soils 30 

veins,  formation  of 31 

R. 

Rain  belts,  temperate  and  tropical 295 

Rainfall,  amount  of 215 

distribution  in  California  and  Montana 290 

in  the  United  .States 215 

most  important 290 

on  tin-  globe,  figure 294 

influence  on  soil  formation 22 

insufficient,  forms  alkali  soils 28 

leaves  lime  behind 28 

natural  disposition  of 216 

Rains,  beating 221 

cold  and  warm 3<>2 

Reclaimable  and  irreclaimable  alkali  lands 534 

Red  foothill  soils  of  California 34 

Red  or  rust-colored  soils 34 

advantages  of.  .                          284 


582  INDEX. 

PACK 

Regur  soils,  Deccan,  India 414 

formation  of 415 

"  guvarayi  "  hardpan 415 

present  production 414 

Reh  of  India , 440 

Reserve  plant-food  in  soils 320 

of  zeolites,  carbonates,  phosphates 321 

Residual  soils 11,13,     22 

Rhizobia,  adaptation  to  symbiosis .  .   154 

inoculation  of  soils  with «, 154 

increase  of  crops  by  inoculation  with 155 

of  legumes 150 

mode  of  infection 154 

varieties  of  forms 154 

Rhubarb,  sensitive  to  alkali 475 

Rhyolites,  soils  from 53 

River  bars,  formation  of 7 

Rivers,  amount  of  dissolved  matters  carried  by 24 

flood-plains  of 13,     14 

sediment  carried  by 24 

waters,  analyses  of,  table,  discussion 23,     24 

white  and  green 4 

Rock  crystal 29 

Rocks  as  soil-formers 47 

chemical  decomposition  of ....     16 

cleavage  of 3 

definition  of  xxix 

disintegration  of,  under  extremes  of  temperature 2 

effects  of  heat  and  cold  on i 

erosion  of  by  sand 10 

forming  minerals 29 

fragments,  rounding  of,  by  flowing  water 6 

Rock  powder 85 

Rock-weathering  in  arid  and  humid  climates 47 

Rohhumus 122 

Rolling  of  soils,  of  influence  of,  on  heat 305 

Root  action,  limitation  of 351 

Root  bacillus,  figure 149,   150 

Root  crops,  effects  of  alkali  upon 474 

Root  development  in  the  arid  and  humid  regions 169  to  176 

Rooting,  deep,  from  proper  irrigation 243,  245 

Roots,  chemical  action  of 21 

force  exerted  by 19 

secrete  carbonic  acid 20 

Root  system  in  the  humid  region  ;  figure 168 

Rotten  Limestone,  soils  from,  analyses 54 

Runoff  of  rain  water ...   216 


INDEX.  583 

PAGK 

Russia,  black  earth  of  ;  roots  and  humus  in 130,  363 

Rye  grass,  giant,  of  Northwest  ;  uses 470 

S. 

Saline  and  alkali  lands,  vegetation  of 527 

plants,  analyses  of  ashes  of 530 

selective  power  of 53  r 

Saline  and  xerophile  vegetation,  similarity  of 528 

Saline  contents  of  waters,  variations  of 250 

solutions,  structural  and  functional  differences  caused  by 528 

vegetation,  general  character  of 527 

Saltbushes,  Australian,  growth  and  use  in  California 469 

of  Great  Basin,  probable  usefulness 468 

Salt-grass  ;  range,  tolerance  of  alkali,  figure 546,  547 

Salton  Basin,  profile  of  salts  in 438 

Salts,  absorption  of,  by  saline  plants 529 

Saltwort  :  range,  tolerance  of  alkali,  figure 540,  542 

Samoa  and  Kamerun  soils,  analyses  by  Wohltmann  ;  method 402 

table  of 404 

Samphire,  Bushy  and  Dwarf  ;  range,  alkali-tolerance,  figure. . .  .538,  539,  540 

Sand  blasts,  effects  on  cobbles 10 

coarse,  effect  of,  on  clays 105 

erosion  of  rocks  by  ;  figure 10 

hammocks,  of  Gulf  coast ...    56 

Sands  of  arid  and  humid  regions,  differences  in 86,  386 

table  of  analyses 387 

Sand,  silt  and  dust 85 

Sandstones 48 

argillaceous 57 

calcareous,  formation   of 56 

rich   soils  from 56 

dolomitic,  often   form  poor  soils 56 

ferruginous,  poor  soils   from 56 

siliceous,  poor  soils  from 55 

varieties  of 55 

xeolitic.  soils  from 57 

Sandstone  soils,  lightness  of 55 

soils,  poor,  of  humid  region 55 

Sand  storms   9 

Sandy  lands,  of  arid  regions,  highly  productive 386 

Sandy  soils 30 

Schone's  elutriator,  figure 90 

Shrinkage,  extent  of,  in  drying  soils  ;  figure 113,  114 

Schiibler  on  calcareous  soils 115 

Sea  water,  average  composition  of,  table 26 

chief  ingredients  useless  to  plants 28 

minor  constituents  of 27 

sources  of  salts  in. .  26 


584  INDEX. 

PAGE 

Sedentary  soils n,  13,  40 

Sedimentary  rocks 47,  48 

Sediment  deposited  by  Mississippi  in  Gulf 7 

Sediments,  exhibition  of,  from  physical  analysis 95,  96 

number  of,  in  physical  analysis 93 

table  of  diameters  and  hydraulic  values 94 

Seeds,  germination  of  309 

Semi-humid  and  semi-arid  region 377,  397 

Serpentine 36 

Sieves,  use  in  physical  analysis  of  soils 88 

Silica,  absorption  and  secretion  by  plants 31 

and  alumina,  soluble  ;  quantitative  relations 385 

solubility  in  water , 31 

soluble,  retained  in  alkali  soils 391 

Silicate  minerals 31 

Silicates  of  soda  and  potash,  soluble , 31 

Silicon,  abundance  of,  in  rocks xxxi 

Silicophile  plants,  a  fiction 522 

Sinkholes 43 

Soapstone 36 

Soda  in  arid  and  humid  regions 394 

Soda,  nitrate  of 66 

Sodium  salts,  leached  out  by  drains  and  rivers 24 

Soil  analysis,  change  of  views  regarding 317 

discrepant  methods  used  in 402 

practical  utility  of 318 

Soil  and  subsoil,  causes  and  processes  of  differentiation 120 

ill-defined 120 

Soil   bacteria,  numbers  of 141 

Soil  character,  recognition  from  native  vegetation 487,  511 

Soil-dilution  experiments 347 

figures 348,  349,  350 

table  of 350 

Soil -examination,   short  approximate  methods  for,  used   at  California 

station 560 

summary  directions  for,  in  field  or  farm 556 

Soil-formation  influenced  by  rainfall 22 

physical  processes  of i 

Soil-forming  processes  accelerated  by  high  temperatures 398 

Soil-grains,  number  of : 99 

surface  of 99 

determination  by  air-flow 99 

by  ' '  Benetzungswarme  " 99 

investigation,  historical  review  of 313 

moisture,  regulation  and  conservation  of 234 

phosphates,  solubility  in  water  ;   Schloesing  fils 332 

probe,  mode  of  using 177 

profiles  in  arid  and  humid  region 165 


INDEX. 


Soil,  samples,  directions  for  taking,  by  Calif.  Station 553 

sedentary  or  residual 1 1 ,  13,  40 

study,  qualifications  needed  for 524 

surveys,  early,  of  Kentucky,  Arkansas  and    Mississippi 316 

temperature,  annual  range  near  surface  in  arctic  and  tropical  regions  303 

change  with  depth  ;   table 303 

influence  of  evaporation  on 307 

influence  of  soil  material 306 

influence  of  surface  conditions, 303 

influence  of  vegetation  and  mulch 305 

tests  by  crop  analysis,  Godlewski,  Vanderyst   337,  338 

by  extraction  with  organic  acids  ;   Dyer,   Maxwell 339 

water,  different  conditions  of 195 

Soils,  acid-soluble  and  water-soluble  portions  most  important 324 

alluvial   12,  13 

ancient,  in  geological  formations xxix 

calcareous,  definition  of 367,  496,  524 

classification  of,  figure 1 1 

colluvial 1 2,  24 

definition  of xxix 

derived  from  various  rocks 49 

effects  of  cn'sting  on 221 

indefinite  action  of  dilute  acids  on 326 

interpretation   of  analyses  ;   Wohltmann 4°3 

physico-chemical  investigation  of 3 '3 

(see  Table  of  Contents) 

Solar  radiation,  influence  of 02 

Solubility,  continuous,  of  soils  in  water 2.S 

King's  table,  rich  and  poor  soils 

Schult/.e's  table,  rich  soil 

Ulbricht's  table,  poor  soil 29 

Solvent  action  of  water  upon  soils 327 

power  of  water '7 

Solubility,  increased  with  nitrogen-content M1 

Sour  grasses '  23 

humus,  antiseptic  properties  of 122 

soils J  22 

Souring  of  soils,  by  cultivation '  23 

Stable  or  farmyard  manure 

composition  <>f,  table 73 

green-manuring  only  substitute 74 

method  of  using,  in  humid  region 74 

physical  effects  of 73 

use  of,  in  the  arid    region 74 

Stalactites  and  stalagmites. ...  4' 

Stassfurt  Salts,  discovery  of . .  . . .     69 

importance  to  agriculture 7° 

origin  of 7° 


586  INDEX. 

PACK 

Stassfurt  Salts,  nature  of 71 

Stonecrops,  succeed  mosses 20 

Stone  fruits,  resistance  to  alkali 478 

Stratified  rocks,  derived  from  crystalline 29 

Stunted  growth,  caused  by  shallow  or  very  heavy  soils  504 

Sturdy  growth  on  calcareous  lands 502,  503 

Subsidence  method 89 

Subsoils,  arid  region 163 

and  deep  plowing 164 

calcareous 162 

rawness  of,  in  humid  climates 163 

Substrata  in  arid  region,  importance  of 173 

faulty,  with  figures 177  to  180 

impervious,  injury  from  ;  figure 181 

leachy 182 

marly 186 

Subterranean  rivers 41 

Sulfate  of  potash,  high-grade 71 

of  soda,  dust  from , 77 

injuriousness  to  plants 77 

occurrence  in  arid  regions 77 

Sulfates,  reduction  of 232 

Sulfuric  acid  in  arid  and  humid  regions 394 

Summer  mulch,  loss  of  humus  in 132 

Sunflower  family,  resistance  to  alkali 473 

Sun's  heat,  penetration  into  the  soil 302 

Surface  crusts,  formation  of in,  117 

physical  analyses  of n8 

Surface,  hydrostatic  and  ground  waters 215 

Surface  waters,  chemical  effects  of  percolation 161 

physical  effects  of  percolation 161 

Swamping  of  alkali  lands,  consequences  of 451,  463 

irrigated  lands,  results  of 231 

Symbiosis,  adaptation  to,  of  Rhizobia 154 

Szek  of  Hungarian  plain 440 

T. 

Tabashir 31 

Talc  and  serpentine 36 

Tap-roots,  moisture  supplied  by 229 

Tea,  failure  on  calcareous  lands 414 

Temperature,  annual  mean  of 289 

conditions,  ascertainment  and  presentation  of 288 

extremes,  on  high  mountains  and  plateaus 288 

of  stellar  space 288 

seasonal,  monthly  and  daily  means 289,  291 

Temporary  vs.  permanent  productive  capacity  of  soils 340 


INDEX. 


587 


PAT.B 

Tennessee  and  Kentucky,  vegetation  and  soil-character 513 

Terraces,  river  and  lake 14 

Testing  penetration  of  irrigation  water 242 

Textile  plants,  tolerance  of  alkali 475 

Thomas  or  basic  slag 64 

Thurman's  physical  theory  of  plant  distribution.    519 

Tillage  ;  effects  of  ;  figure 109,  1 10 

how  maintained  in  nature 1 1 1 

Titanium  in  soils xxxi 

Time  of  acid-digestion,  different  ;  table 342 

Tolerance  of  alkali  by  culture  plants 463 

alkali  plants  ;  table 548,  549 

Topography,  influence  of,  on  climate 293 

Trachytes 53 

Trona,  Urao 77 

Tropical  soils 398 

are  highly  leached 400 

often  highly  colored  with  iron 400 

do  not  need  early  fertilization 399 

humus  in  ;  abundant,  but  low  in  nitrogen 399 

few  determinations  made 399 

possible  calculation  of 399 

investigations  of 401 

laterites,  not  always  rich  in  iron 4cxi 

mostly  have  low  plant-food  percentages 400 

resemble  the  "  nimble  penny." 400 

Tubercles  of  legumes,  figures 151,    154 

Tufa,  calcareous }  i 

Tussock  grass,  food  value  of J7<) 

range,  alkali-tolerance,   figure 536,  537 


Ulmin  substances 122 

Underdrainage,  advantages  of ;;vs 

Underdrains,  effects  of 234 

Unhumified  organic  matter  does  not  nitrify i.;S 

Unhumified  vegetable  matter,  utility  of.  .  .               135,  3^0 

United  States,  good  field  for  comparative  soil  study 524 

Upland  and  lowland  growth  in  arid  and  humid  regions 515 

Usar  lands  of  India,  character  of 440 

not  all  alkali  lands 440 

V. 

Vegetative  belts,  lime  a  governing  factor  of 492 

Virgin  lands,  advantages  of  soil  study  in 318 

Virgin  soils,  analysis  by  extraction  with  strong  acids 340 

Yivianite 65 


588 


INDEX. 


Volatile  part  of  plants xxxii 

Volcanic  ash,  form  soils  rapidly  ;  soils  from 20,  52 

Volcanic  glass 53 

Volume  of  soils,  changes  on  wetting  and  drying 122 

Volume-weight  of  soils 107 

W. 

Walnut,  black,  a  lime-loving  tree 490  to  497 

tolerant  of  white  alkali 479 

Washing-away  and  gullying  of  land 217 

Water,  capillary 201 

ascent  in  soil  columns,  figure. . 202,  205 

uniform  sediments,  figure 204,  207 

held  at  different  heights  in  soil  column,  table 208 

expansion  and  contraction  in  absorbing 208,  209 

maximum  and  minimum  of  waterholding  power,  ter- 
mination of  ;  figure 202,  207 

movements  in  moist  soils 210 

carbonated,  solvent  power 17 

carrying  power 14 

controlling  factor  of  soil  temperature 301 

density  of 190 

effects  of  flowing 5 

Water-extraction  of  soils,  practical  conclusions  from 332 

Water,  hard 41 

hygroscopic 1 96 

of  land-locked  lakes 27 

loss  of,  by  irrigation  in  shallow  furrows 240 

physical  factors  of 188 

regulation  of  temperature  by 191 

relations  to  heat 189 

requirements  of  growing  plants 192 

plants  in  arid  regions 195 

sidewise  penetration  of,  in  soils 241 

of  soils  (chapters  on) 188,  215,  234 

,      solvent  action  upon  soils 327 

solvent  power 17,  191 

Water-soluble  plant-food 321 

specific  heat  of 190,  191 

table 227 

vaporization  of 191 

Watery  soil  extracts,  from  European  soils  ;  tables 327,  329 

American  soils,  King 329,  330 

Wave  action  on  shores,  figure 7 

Weathering,  by  oxygen,  carbonic  acid,  water 16,  17 

"  in  humid  and  arid  regions 2,  86 

Weight  of  soils,  per  acre-foot 107 


INDEX. 


589 


White  soils,  nature  of,  in  humid  regions 285 

in  arid  regions 286 

Wind  deposits 105 

Winds,  action  of,  in  forming  soils 8 

cyclones,  and  anticyclones 293 

effects  of,  in  deserts 8 

heat  the  cause  of 291 

land  and  sea  breeze 291 

trade,  and  monsoons 291,  292 

Winter  irrigation 236 

Wire-basket  tests,  of  Bureau  of  Soils 337 

X. 

Xerophile  vegetation,  similarity  to  saline 529 

Y. 

Yazoo  bottom,  soils  of 1 16 

Yazoo  •'  buckshot  "  and  Arroyo  Grande  soils 345 

Z. 

Zeolites,  decomposition  by  acids 36,  38,  39 

exchange  of  bases  in  analcite  and  leucite 37 

formation  of 37 

importance  in  soils 38 

rocks  cemented  by 38 

Zeolitic  sandstones 57 


AUTHORS    REFERRED  TO. 


[NoTE. — In  cases  where  no  special  credit  is  given  in  this  volume  for  investigations  made  or  data 
given  from  the  Southwestern  States  and  the  Pacific  Coast,  these  should  be  understood  as  work  done, 
mostly  under  the  writers  direction,  or  by  himself  and  assistants,  in  connections  with  the  geological 
survevs  of  Mississippi  and  Louisiana,  as  well  as  the  Tenth  Census  of  the  United  States,  by  Ore. 
Kugene  A.  Smith  and  R.  H.  Loughridge;  the  chemical  work  for  the  Pacific  Northwest,  under  the 
auspices  of  the  Northern  Transcontinental  Survey,  by  M.  K.  Jaffa  and  (Jeo.  K.  Colby;  that  in  Cal- 
ifornia, at  the  Experiment  Station,  by  the  latter  two,  Dr.  R.  H.  I.ougluidge,  and  temporary  assistants. 
It  would  be  impossible  to  segregate,  without  excessive  prolixity,  the  credit  to  be  assigned  to  each 
of  these  participants.] 


A. 

Adametz,  I,.,  142,  281. 
Agassiz,  L.,  4. 
Aso,  K.,  383. 

H. 

Bamber,  — ,  401,  410,  414, 
Batholomew,  J.  (i.  294. 
Bejerinck,  M.  \V.,  151,  156. 
Blumtritt,  K.,  276. 
Bonnier,  (J.,  521. 
Bottcher,  ().,  393. 
lioussingault,  J.  H.,  151,  276,  313. 
Brick,  — ,  528. 
Brock,  see  Morck,  I). 
Burri,  K.,  148. 
Butler,  ().,  151. 

C. 

Cameron,  F.  K.,  580,  466,  5^2,  533. 
Clarke,  F.  \V.,  XXX,  XXXI,  23. 
Colby,  (I.  F.,  note  above. 
Colmore,  C.  A.,  448. 
Contejean,  Ch.,  521,  523,  531. 
Coville,  F.  V.,  536. 
Crochetelle,  J.,  146,  147. 

I). 

Dai  ton,  X.  II..  10. 
Darwin,  Ch.,  158. 
Davy,  J.  B..  535. 
Deherain,  1'.  I'.,  146,  147. 
I  Miner.  \V.,  127. 


Djemil,  — ,  159. 
Duclaux,  P.  F.,  144. 
I)uggar,  J.  F.,  155. 
Dumont,  J.,  146,  147. 
Dyer,  1?.,  339,  357. 

E. 

Ebermayer,  F.,  279,  305. 
Fckart,  C".  F.,  212. 
Fichorn,  — ,  327. 
Frmann,  (i.  A.,  303. 

F. 

Fawrett,  W.,  355. 
Fischer,  Hugo,  I  56. 
Fliche,  P.,  520,  521. 
Forbes,  R.  II.,  219. 
Fortier,  S.,    194,  254. 
Kraenkel,  I..,  142. 
Frank.  A.,  151. 
Fuelles,  P.,   281. 
Furry,  F.  F.,  73. 
Furuta,  T.,  383. 

C,. 

Cieikie,  J..   14. 
Cierlach,  — ,  156. 
C.ilbert,  ( ',.  K  ,  2. 
('•ilbert.   I.  H..  151,  I')2. 
(iodlewski,  F.,   ^37,  393 
(loss,  A.,  376,  530. 

591 


592 


AUTHORS  REFERRED  TO. 


Grandeau:  L.,    132,    133,  139,  357,   520,    Liebig,  J.  von,  150,  313. 

521.  Liebscher,  G.,  354. 

TT  Lipman,  J.  G.,  156. 

Loeb,  J.,  380. 

Haberlandt,  F.,  310.  Loew,  O.,  23,  42,  38',  383. 

Hall,  A.  D.,  210,  227.  Loughridge,    R.    H.,   87,    207,  213,  214, 

Hare,  R.  F.,  378.  24O)  259,  340  to  342,  385,  430,  462,  466, 

Harper,  R.  M.,  494.  5!3)  535>  56o. 
Hartwell,  B.  L.,  123. 

Headden,  H.  P.,  18.  M. 

Hedin,  Sven,  9.  ,          ,  ,        . 

TT  „  •       ,   T-  Maercker,  M.,  65,  369. 

Hellnegel,  F.,  130,  151,  192.  ,,          TT   Tr       J  J  y 

Mann,  H.  H.,  401,  410,  413. 
Hennci,  200. 

Manson,  M.,  294. 
Hillman,  F.  H.,  536. 

T...  Maxwell,  W.,  339. 

Hiltner,  L.,  154.  ..       T_    .,_.      joy  0 

May,  D.  W.,  42,  380. 
Hoffmann,  R.,  528. 

TT  i ,    T  Mayer,  A.,  199,  207,  209. 

Hohl,  J.,  143.  '     '  y- 

Mayo,  N.  S.,  141. 
Hunt,  T.  S.,  23.   .  M  n   t.    o 

Mazurenko,  D.  P.,  87. 

J.  Means,  T.  H.,  248,  478. 

Merrill,  G.  P.,  2,  13,  167. 

Jaffa,  M.  E.,  135,  381,  450,  530.  ...  , ,      ,     ....  ,T 

T  u  o   wf    vv-tVi       o  Middendorff,  V.,  441. 

Johnson,  S.  W.,  XXV,  60,  380.  -„.      ,     ..  ,  '        . 

Mitscherhch,  E.  A.,  99,  199. 

jr  Miquel,  P.,  142,  281,  359. 

Mohr,  Chas.,  489,  511. 

Katayama,  T.,  383.  Moore,  G.  T.,  154. 

Kearney,  T.  H.,  532.  Morck,  D.,  1 54. 

Kedzie,  R.  C.,  343,  375.  Miiller,  A.,  449. 

Kellner,  O.,  393.  Miiller,  P.  E.,  122,  184. 

King,  F.  H.,  99,  108,  109,  168,  192,  193,  Miintz,  A.,  142,  355,  370,  401,  402,  406  to 

210,    211,    212,    224,    228,236,305,    325,  4i0- 

32°>  332-  Murray,  John,  23,  24. 

Kinsley,  J.  S.,  143.  Myers,  H.  C.,  6,  144. 
Knop,  W.,  197. 
Koch,  R.,  156,  281.  N. 

Kossovitch,  P.,  761. 

Naegeh,  C.  v.,  129. 
Kosticheff,  P.,  130,  157. 

-  •*       J  Nasraoka,  M.,  6q,  wi. 

Krober,      ,  156. 

Nobbe,  F.,  154. 
Krocker,  F.,  22. 

Kuntze,  O.,  67,  68.  O. 

L.  Osterhout,  W.  J.  V.,  533. 

Ototzky,  L.,  265. 
Ladd,  E.  F.,  131,  133.  134,  141. 

Langley,  S. Y,  i*  °WCn'  D"  D"  3'6'  3'7'  343>  ™ 

Lawes,  J.,  151,  192. 

Lea,  E.  C.,  387. 

Leather,  J.  W.,  401,  410,  411,  412,  414  to    Peter,  A.  M.,  175. 

417,  440.  Peter,  R.,  316,  317,  343. 

Lemberg,  J.,  272  Pichard,  P.,  147. 

Lesage,  M.,  528.  Porter,  J.  L.,  23,  24. 

Letheby,  H.,  23.  Pumpelly,  R.,  no. 


AUTHORS  REFKRRKD  TO.  593 

R.  Traphagen,  F.  W.,  23. 

Rafter,  G.  W.,  217.  Tuxtn'  C-  F-  A-  l84- 

*  Ramann,  E  tj 

Reade,  T.  M.,  41. 

.     ,,       ,  Udden,  J.  A.,   roo. 

Regnault,  V  .,  20. 

Ulbricht,  R.,  328. 
Reichert,  E.,  276. 

Richthofen,  F.  von,  no.  V. 

Risler,  E.,  354.  Vanderyst,  II.,  338. 

Rosenberg,  S.,  528.  Ville,  G.,   151. 

Rousseaux,  E.,  355,  370,  401,  402,  406  to    Voelcker,  J.  A.,  22,  410. 

4<o.  Vogel,  J.  H.,  156. 

Rud/.inski,  D.,  87. 

Russell,  I.  C.,  24.  W- 

c  Wagner,  P.,  65. 

Ward,  M.,  144. 
Saussure,  II.  I'-,  de,  i  So.  ..,     .  ,,         o        s 

\\anngton,  R.,  rob,  140. 
Schimper,  A.  F.  W.,  1523,  528.  ...  ire     wv 

Washington,  II.  S.,  XXX. 

Schloesing,  Th.,  59,  in,  354.  Way,  J.  T     22,73 

Schloesing,  Th.,  tils,  332,  393.  w'eb'er;  A" u~.',  4SO. 

Schmidt,  C.,   23.  Wheeler,  II.  J.,  123. 

Whitney,  M.,  94,  195-   *O7,  3l6,  32l,  3y>, 

Schubler,  J.  J.,  116,  197,  313. 

Schultze,  II,  3=8,329-  WUfartlJ V  151. 

Sc-ton,  K.T.,  159,  .00.  Williams,  W.  K.,  60,  100. 

Winognulsky,  S.,  .46,  156. 

Wohltmann,    F.,    355,    370,    401,  402  to 
Smith,  E.  A.,  511.  .,05,406,4.6. 

Snyder,  H.,  131.  .33,  .34,  '39-  W()1|f>  ,.      ,_,_  7J- 

Wollnv/E."   'no,  .,3,  .25,  .47,  .59,   195, 
S.^kbnc'ge,  II.  E.,  307.  308-  2(  ,8li  jSj(;  305;306. 

Wullner, -,  198. 

.Sft/ht-i.-n'ich,  A.  \  .,   222.  ...       ,        .. 

\\  under,  ( •.,  }2~. 
Stut/.er,  A.,  149. 

V. 
T. 

Voder,  P.  A.,  92. 
Thurmann,  J.,  519,  520. 
Tolm.m,  I..  M.,  jS7. 
Toum.-v,  !.  W.,   216.  /oiler,  P.  H.,  22. 


*  Tins  writi-r'*  v.ihi.ihlo  "  Uodcn  Kundc  "  (.1.^5)  untorl-iu.itcly  came  to  liaud   too  late  to  be  con- 
sidered in  this   volume. 


Printed  in  the  Unitdl  States  of  America. 


8515      12 


University  of  California 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 

305  De  Neve  Drive  -  Parking  Lot  17  •  Box  951388 

LOS  ANGELES,  CALIFORNIA  90095-1388 

Return  this  material  to  the  library  from  which  it  was  borrowed. 


Biom&w 


RECEIVED 


gr    APR 

F<trm  L-9-15tn-2,'36 


UNIVERSITY  of  CAUFORKIA 

AT 

LOS  ANGELES 
LIBRARY 


A     001  075  699     7 


'00683  0714 


